Forest structure and function strongly depend on and concurrently influence environmental conditions. Tree performance is generally governed by its genetics and environment; thus, recent hotspots in this field include tree genotype × environment, phenotype × environment, and functional trait × environment interactions. The editorial, review, and 22 original research articles in this Special Issue, “Tree ecophysiology in the context of climate change”, highlight ecophysiological phenomena (e.g., climate hormesis, seed germination, tree mortality), processes (e.g., tree metabolism, photosynthate allocation, nutrient uptake and transport), indicators (e.g., carbon sequestration, pollutants), measurements (e.g., thermal time methods, soil quality indices, vegetation spectral index, and near-infrared leaf reflectance), and modeling (e.g., climate correlations with tree growth, photosynthetic phenology, hydraulic strategies, OliveCan model) in the context of global climate change. Understanding forest–environment interactions from an ecophysiological perspective as climate changes provides insights into species fitness in suboptimal environments, species competition for limited resources, and phylogenetic divergence or convergence of species, and predicting species distributions.
Woody plants contribute to the stability and productivity of terrestrial ecosystems and are significantly affected by climate change. According to the concept of environmental hormesis, any environmental stressors can cause hormesis, that is, stimulation in low doses and inhibition in high doses. Numerous studies have demonstrated plant hormesis under low doses of various abiotic stressors. However, the hormetic responses of woody plants to abiotic stressors from climate change are insufficiently studied. This review analyses data on the stimulating effects of low doses of climate stressors in experiments and in real ecosystems. Numerous laboratory and field experiments show that single and combined exposure to various climate stressors (temperature, humidity, and elevated carbon dioxide concentrations) can cause hormesis in various species and functional types of woody plants, which can be accompanied by hormetic trade-offs and preconditioning. In addition, there is evidence of climate hormesis in woody plants in ecosystem conditions. Field experiments in various ecosystems show that elevated temperatures and/or precipitation or elevated carbon dioxide concentrations causing hormesis in dominant tree species can stimulate ecosystem productivity. Moreover, climate hormesis of the growth and reproduction of dominant forest tree species contributes to the spread of forests, that is, climate-driven ecological succession. The main commonalities of climate hormesis in woody species include: (1) Low-dose climate stressors cause hormesis in woody plants when strong (limiting) stressors do not affect plants or these limiting stressors are mitigated by climate change. (2) Hormesis can occur with the direct impact of climatic stressors on trees and with the indirect impact of these stressors on plants through other parts of the ecosystem. (3) Climate stressor interactions (e.g., synergism, antagonism) can affect hormesis. (4) Hormesis may disappear due to tree acclimatization with consequent changes in the range of tolerances to climate factors. This review highlights the need for targeted studies of climate hormesis in woody species and its role in the adaptation of forest ecosystems to climate change.
The Betula genus contains pentacyclic triterpenoid betulin known for its environmental adaptation and medicinal properties. However, the mechanisms underlying betulin biosynthesis responding to climate change remain unclear. In this study, the role of epigenetic modification (DNA methylation) in betulin biosynthesis was examined and how climatic factors influence it. Whole-genome bisulfite sequencing was performed for greenhouse-grown Chinese white birch (Betula platyphylla Sukaczev) treated with DNA methylation inhibitor zebularine (ZEB) and a natural birch population in Northeast China. ZEB treatment significantly affected the CHH methylation level of transposable elements and betulin content in a hormesis dose-dependent manner. The methylation and expression of bHLH9, a key transcriptional factor controlling betulin biosynthesis, were also consistently affected by ZEB treatment as a hormetic dose–response. In the natural population, there was a positive correlation between promoter methylation of bHLH9 and summer precipitation, while winter temperature was negatively correlated. Thus climate-dependent methylation of bHLH9 regulates the expression of downstream genes involved in betulin biosynthesis. This study highlights the role of environmental signals to induce epigenetic changes that result in betulin production, possibly helping to develop resilient plants to combat ongoing climate change and enhance secondary metabolite production.
The future health and productivity of tree species in the northern hardwood forest of eastern North America are uncertain considering changes in climate and pollution loading there. To better understand the trajectory of the northern hardwood forest, we studied the growth of three tree species emblematic of it: sugar maple (Acer saccharum Marsh), American beech (Fagus grandifolia Ehrh.), and yellow birch (Betula alleghaniensis Britton), plus a fourth species, red maple (Acer rubrum L.), whose abundance has increased in the region. We also analyzed the link between growth and several factors for 690 trees in 45 plots throughout Vermont, USA: tree age and size, site elevation, and climate and acid deposition variables. Throughout their chronologies (1945–2014), all four species exhibited increasing growth followed by plateaued growth indicative of a maturing forest. For all species, summer moisture was positively correlated with growth, summer temperature was negatively associated with growth, and winter moisture or snow were positively correlated with growth. This last association was expected for sugar maple. However, our data suggest that winter snowpack may be more broadly relevant in sustaining tree growth in a region where snow has historically insulated the soil from freezing that can damage roots and lead to reduced aboveground growth. Measures of pollution deposition were also correlated with growth for all species except American beech—a species with documented tolerance to pollutant inputs. Of the four species studied, red maple had the fewest associations with environmental variables, which suggests that it may be less susceptible to growth reductions as the climate changes.
Seasonal patterns of wood formation (xylogenesis) remain understudied in mixed pine–oak forests despite their contribution to tree coexistence through temporal niche complementarity. Xylogenesis was assessed in three pine species (Pinus cembroides, Pinus leiophylla, Pinus engelmannii) and one oak (Quercus grisea) coexisting in a semi-arid Mexican forest. The main xylogenesis phases (production of cambium cells, radial enlargement, cell-wall thickening and maturation) were related to climate data considering 5–15-day temporal windows. In pines, cambium activity maximized from mid-March to April as temperature and evaporation increased, whereas cell radial enlargement peaked from April to May and was constrained by high evaporation and low precipitation. Cell-wall thickening peaked from June to July and in August–September as maximum temperature and vapour pressure deficit (VPD) increased. Maturation of earlywood and latewood tracheids occurred in May–June and June–July, enhanced by high minimum temperatures and VPD in P. engelmannii and P. leiophylla. In oak, cambial onset started in March, constrained by high minimum temperatures, and vessel radial enlargement and radial increment maximized in April as temperatures and evaporation increased, whereas earlywood vessels matured from May to June as VPD increased. Overall, 15-day wet conditions enhanced cell radial enlargement in P. leiophylla and P. engelmannii, whereas early-summer high 15-day temperature and VPD drove cell-wall thickening in P. cembroides. Warm night conditions and high evaporation rates during spring and summer enhanced growth. An earlier growth peak in oak and a higher responsiveness to spring–summer water demand in pines contributed to their coexistence.
Climate change is causing more frequent and severe climatic events, such as extreme heat and co-occurring drought, potentially accelerating tree mortality. Which tree species will cope better with those extreme events is still being researched. This study focuses on heat as a physiological stress factor and interspecific variation of thermal tolerance and sensitivity traits in 15 temperate coniferous and broad-leaved tree species. We investigate (1) whether thermal tolerance and sensitivity traits correlate with a drought-related physiological trait, particularly the leaf turgor loss point (πtlp, wilting point), and (2) how thermal tolerance and sensitivity traits co-vary within different tree-functional types classified by morphological and physiological traits of the leaf, i.e., leaf mass per area (LMA) and percentage loss of area (PLA). The study was carried out in the Traunstein Forest Dynamics Plot of the ForestGEO network in Germany. The temperature response of the maximum quantum yield of photosystem II (F v/F m) on leaf discs was determined, from which various physiological leaf traits were estimated, one of which is the breaking point temperature (T 5), the temperature at which F v/F m declines by 5%. Additionally, the temperature of 50% (T 50) and 95% (T 95) decline in F v/F m was evaluated. The decline width between T 50 and T 5 (DWT50−T5) was taken as an indicator of the species’ thermal sensitivity. The breaking point temperature ranged from 35.4 ± 3.0 to 47.9 ± 3.9 °C among the investigated tree species and T 50 ranged between 46.1 ± 0.4 and 53.6 ± 0.7 °C. A large interspecific variation of thermal tolerance and sensitivity was found. European ash (Fraxinus excelsior L.) was the most heat-sensitive species, while Wild cherry (Prunus avium L.) was the least heat-sensitive species. Species with a more negative πtlp tended to have a higher breaking point temperature than species with a less negative πtlp. A lower thermal sensitivity characterized species with a higher LMA, and high PLA was found in species with low thermal sensitivity. Accordingly, species with thicker and tougher leaves have lower thermal sensitivity which coincides with a lower wilting point. We conclude that species that develop drought-adapted foliage can cope better with heat stress. Further, they might be able to maintain transpirational cooling during combined heat and drought stress, which could lessen their mortality risk during climatic extremes.
Interactions between water and carbon dynamics underlie drought-related tree mortality. While whole-tree water relations have been shown to play a key role in the response to and recovery from drought, the role of nonstructural carbohydrates (NSC) and how their storage and allocation changes surrounding drought events deserves further attention and is critical for understanding tree survival. Here, we quantified in situ NSC responses of temperate forest trees to the 2016 drought in the northeastern United States. Sugar and starch concentrations were measured in the stemwood of five tree species from 2014 to 2019, which allowed us to monitor NSCs in relation to climatic conditions before, during, and after the natural drought. We found that immediately following the drought, measured stemwood NSC concentrations decreased. However, NSC concentrations rebounded quickly within three years. Notably, trees allocated proportionally more to starch than to sugars following the 2016 drought. In winter 2017, starch comprised 45% of total stemwood stores, whereas starch made up only 1–2% in other years. Further, we modeled and assessed the climatic drivers of total NSC concentrations in the stem. Variation in total NSC concentrations was significantly predicted by the previous year’s temperature, precipitation, and standardized precipitation-evapotranspiration index (SPEI), with stemwood concentrations decreasing following hotter, drier periods and increasing following cooler, wetter periods. Overall, our work provides insight into the climatic drivers of NSC storage and highlights the important role that a tree’s carbon economy may play in its response and recovery to environmental stress.
Stored nonstructural carbohydrates (NSC) indicate a balance between photosynthetic carbon (C) assimilation and growth investment or loss through respiration and root exudation. They play an important role in plant function and whole-plant level C cycling. CO2 elevation and nitrogen (N) deposition, which are two major environmental issues worldwide, affect plant photosynthetic C assimilation and C release in forest ecosystems. However, information regarding the effect of CO2 elevation and N deposition on NSC storage in different organs remains limited, especially regarding the trade-off between growth and NSC reserves. Therefore, here we analyzed the variations in the NSC storage in different organs of Chinese fir (Cunninghamia lanceolata) under CO2 elevation and N addition and found that NSC concentrations and contents in all organs of Chinese fir saplings increased remarkably under CO2 elevation. However, N addition induced differential accumulation of NSC among various organs. Specifically, N addition decreased the NSC concentrations of needles, branches, stems, and fine roots, but increased the NSC contents of branches and coarse roots. The increase in the NSC contents of roots was more pronounced than that in the NSC content of aboveground organs under CO2 elevation. The role of N addition in the increase in the structural biomass of aboveground organs was greater than that in the increase in the structural biomass of roots. This result indicated that a different trade-off between growth and NSC storage occurred to alleviate resource limitations under CO2 elevation and N addition and highlights the importance of separating biomass into structural biomass and NSC reserves when investigating the effects of environmental change on biomass allocation.
Persistent and severe drought induced by global climate change causes tree mortality mainly due to the hydraulic imbalance of conduit systems, but the magnitude of injury may be species dependent. A water-exclusion experiment was carried out on seedlings of two tree species with distinct characteristics, i.e., Fraxinus mandshurica and Larix gmelinii to examine hydraulic responses of leaf, stem, and root to drought stress. The two species displayed different hydraulic strategies and related traits in response to drought stress. L. gmelinii reduced its leaf hydraulic conductance by quick stomatal closure and a slow decline in leaf water potential, with a more isohydric stomatal regulation to maintain its water status. In contrast, F. mandshurica was more anisohydric with a negative stomatal safety margin, exhibiting strong resistance to embolism in stem and leaf-stem segmentation of hydraulic vulnerability to preserve the hydraulic integrity of stem. These differences in hydraulic behaviors and traits between the two species in response to drought stress provide a potential mechanism for their co-existence in temperate forests, including which in the forest modeling would improve our prediction of tree growth and distribution under future climate change.
Plants hold biochemical and physiological mechanisms to withstand drought conditions. Generally, depending on water deficit interval, plant rehydration relies on how it can retain growth or a positive water balance—or rarely both. In this study, two species of Hymenaea, one from the Amazon and the other from the Brazilian Cerrado, were investigated for their physiological mechanism associated with growth rehydration upon short-term exposure to drought stress. Our findings demonstrate that Hymenaea courbaril tends to invest in nitrogen to the detriment of carbon compounds, − as it is limited by lower net photosynthesis − and adjust root growth to attenuate drought stress responses. In contrast, Hymenaea stigonocarpa takes advantage of higher water potential and a basal rate of lower net photosynthesis to support aboveground growth under such conditions. Hence, it is postulated that there are distinct ways of controlling water status and growth between H. courbaril and H. stigonocarpa, which are determined either by the ability of the species to keep net photosynthesis at low levels of water content or by favoring the accumulation of nitrogen compounds. Both mechanisms were effective with regards to water use efficiency and thus it is reasonable to suggest that strategies are not exclusive and may work under adverse conditions, as observed in Amazon and Brazilian Cerrado biomes.Query
Seventeen morphological and anatomical characteristics of the leaves were selected from five natural populations to explore the variation in leaf traits of Litsea coreana var. sinensis and the effects of geographical environment on these variations. Nested analysis of variance, multiple comparisons, principal component analysis (PCA), and correlation analysis were conducted to explore the variations within and between populations and their correlation with geographical and climatic factors. Significant differences in the 17 leaf traits were observed within and among populations. On average, the relative contribution of within population variation to total variation was 24.8%, which was lower than among population variation (54.6%). The average differentiation coefficient of the traits was 65.8%, and the average coefficient of variation 11.8%, ranging from 6.7% for main vein thickness to 21.4% for petiole length. The PCA results showed that morphological characteristics were divided into two categories, and the level of variation was greater than that of leaf anatomy. Most of the leaf traits were significantly correlated with geography and climate and showed a gradual variation with longitude, latitude, and altitude. In areas with high temperatures, less rainfall, and strong seasonal rainfall, the leaves are larger, longer and thicker. This study shows that variations in leaf traits of L. coreana var. sinensis mainly come from variations among populations. The level of trait differentiation among populations is high and the level of variation within populations low. These findings help further understand leaf morphological characteristics of this species and can provide a valuable reference for the protection and sustainable utilization of this natural resource.
Tree competitiveness generally depends on trait plasticity in response to environmental change. The effects of nitrogen (N) and phosphorus (P) on leaf trait variability by species is poorly understood, especially in China’s subtropical forests. This study examined the seedling leaf traits and net primary productivity of all trees ˃5 cm DBH of two dominant species, Schima superba and Castanopsis carlesii, in an evergreen broadleaved forest fertilized with nitrogen (+ N), phosphorus (+ P), and nitrogen plus phosphorus (N + P). The effect of N on seedling leaf traits was stronger than P, while fertilization in general was species dependent. Leaf mass per unit area decreased with N for S. superba seedlings but not for C. carlesii. Leaf N, P, and N/P ratios changed with N addition for both species. All four N fractions of carboxylation, bioenergetics, cell wall, and other N metabolites in C. carlesii leaves responded significantly to fertilization, while only the cell wall in S. superba leaves responded. Other leaf functional traits, including light-saturated photosynthetic rates, water, N, and P use efficiencies, chlorophyll and nonstructural carbohydrate contents increased with N addition in S. superba and by P addition in C. carlesii. Canopy closure at the stand-level increased due to N. Litter biomass and relative growth rate of S. superba was not affected by any treatments, while both for C. carlesii significantly decreased with N + P addition. Collectively, nutrient limitation may vary at a small scale among species in a subtropical forest based on their responses of seedling traits and net primary productivity to fertilization. Seedling traits are not correlated with the net primary productivity of larger trees except for N fractions, because low light conditions induced by fertilization reduces the proportion of N allocated to photosynthesis in seedlings. In addition, acclimation differences of tree species may increase the uncertainty of community succession.
The effects of long-day photoperiod on growth, photosynthetic fluorescence, carbon and nitrogen metabolism, and yield of Dendrocalamopsis oldhami and the compensation effects of fertilization were investigated. A completely randomized design was used with two light factors (bamboo culms cultivated in solar greenhouse under long-day [Ls] and short-day [Ln] treatments); two organic nitrogen fertilizer levels (application of organic fertilizer [OF] and no organic fertilizer [NF]); and three nitrogen fertilizer levels (Low [N0], medium [N1] and high nitrogen [N2]). Leaf chlorophyll and fluorescence parameters (φPo, PIABS, and ETo/CSm) decreased and DIo/CSm increased in Ls compared to Ln. Indole acetic acid (IAA) and gibberellic acid (GA3) levels decreased, whereas abscisic acid (ABA) increased. Leaf area decreased and leaf dry mass increased. The contents of carbon and nitrogen metabolism-related enzymes (nitrate reductase, glutamine synthetase, amylase, and sucrose synthase) and products (total nitrogen, organic carbon, soluble sugar, and starch) increased. Single bamboo shoot weight and diameter at breast height decreased, whereas shoot quantity and total yield increased. Fertilizer application significantly affected physiological growth and yield in the two light treatments, thus promoting carbon and nitrogen metabolism. The φPo, PIABS, IAA, and GA3 contents increased slightly, whereas ABA levels decreased. Shoot quantity, individual weight, and total yield improved. IAA, soluble sugar, and total yield to organic manure and light were lower than those of nitrogen levels (FN > FL, FO). Other indicators showed lower responses to different fertilization treatments than the light factor (FL > FN, FO). The ability of D. oldhami to alter its morphological and physio-biochemical traits and yield in response to variations in light applications may translate into high phenotypic plasticity. Fertilization significantly improved photoplasticity of D. oldhami. Under Ls, D. oldhami had high metabolic rates, was easily inhibited by light, and showed accelerated leaf senescence, and shoot quantity and total output increased. However, the quality of individual shoots decreased. Different fertilization treatments affected D. oldhami differently under the two light intensities. Ls sensitivity to nitrogen was higher. Fertilization could delay leaf dormancy and senescence under Ls treatment. Organic fertilizer addition could improve yield more effectively, with OFN1 being the optimal fertilization level.
The objective was to examine the effects of optimal leaf nitrogen levels > 2.0% and suboptimal levels ˂ 2.0%, nitrogen nutrition on net photosynthetic rate, stem diameter increment, height growth increment and acorn mass of pedunculate oak during 2010 in the absence of drought stress and during 2011 under the impact of moderate drought stress. According to the results, moderate drought stress significantly reduced net photosynthetic rate, stem diameter increment and height growth increment, while acorn mass was not affected. Suboptimal nitrogen nutrition significantly reduced the net photosynthetic rate and stem diameter increment only in the wet year, acorn mass in both wet and dry years, while height growth increment was not significantly reduced by suboptimal nitrogen nutrition in either year. The results indicate that optimal nitrogen levels can stimulate photosynthetic rate and stem diameter increment of pedunculate oak only in the absence of moderate drought stress. Moreover, the results show that moderate drought stress is a more dominant stressor for photosynthesis and growth of pedunculate oak than suboptimal nitrogen nutrition, while for acorn development, it is the more dominant stressor.
Mimosa tenuiflora and Piptadenia stipulacea are commonly accepted as drought-tolerant species but little is known about their response to drought followed by rehydration. Therefore, the interplay between leaf water potential and osmotic adjustment on photosynthetic and growth parameters of these species was examined. A greenhouse study was conducted in a split-plot design with two water conditions in the main plots (control; drought followed by rehydration), and eight sampling times in the subplots (1, 4 and 7 days of drought, and 1, 3, 6, 12, and 17 days of rehydration). Plant water status and biochemical changes were assessed as well as leaf gas exchange and subsequent growth. Under drought stress, both species maintained a low leaf water potential throughout the day by accumulating compatible solutes, thus allowing a rapid and full recovery of water status when rehydrated. Although these plants minimized water loss by closing their stomata, neither showed stomatal limitations to photosynthesis. The inhibition of this process during drought was possibly related to mesophyll limitations as well as to a reversible downregulation of photosystems, along with adjustments of their stoichiometry. Water deficits also triggered morphological adaptations at the whole plant level, leading to reduced growth, mainly of the shoots in M. tenuiflora and the roots in P. stipulacea.
Understanding what environmental factors are genetically linked to a phenological event is critical for predicting responses to climate change. Photosynthetic phenology often varies among a species of evergreen conifers due to local adaptation. However, few empirical studies have revealed relevant relationships between climatic factors in provenance environments and photosynthetic phenology. This study evaluated the effects of environmental conditions of the growing site and seed source provenance on the seasonal changes in maximal photochemical quantum yield of photosystem II (F v/F m) in a common garden experiment with 2-year-old seedlings of Sakhalin fir (Abies sachalinensis), a representative species with local adaptation, from four seed source provenances. A logistic model was constructed to explain the seasonal variation of F v/F m from July to October and the relationships between the estimated model parameters and representative factors featuring provenance environments were evaluated. The landscape gradient of the detected model parameters responsible for the provenance environments was visualized in a map of the distribution area. The lowest temperature was the most plausible factor in the growing environment to explain the seasonal changes of F v/F m. Among the representative meteorological factors of provenance environments, the lowest temperatures in July showed significant relationships with two model parameters, explaining the lower limit of F v/F m and the higher sensitivity of autumn F v/F m decline. The estimated spatial maps of model parameters consistently showed that the higher the lowest temperature in July in the provenance environment, the lower the F v/F m in October and the greater the decrease in the autumn F v/F m decline. Therefore, the lowest summer temperature could be associated with the local adaptation of autumn photosynthetic phenology in A. sachalinensis.
The stability of monocultural, even-aged spruce forests at lower altitudes in Central Europe is seriously threatened by the prospects of global climate change. The thermostability and water use efficiency of their photosynthetic apparatus might play a vital role in their successful acclimation. In this study, photosystem II (PSII) performance (OJIP transient, rapid light curves) and thermostability were analyzed in Norway spruce (Picea abies (L.) Karst.) throughout the growing season of the exceptionally warm year 2018 (May–September) in the Western Carpathians, Slovakia. These measurements were accompanied by analysis of pigment concentrations in the needles. In addition, gas-exchange temperature curves were produced weekly from June until September to obtain intrinsic water use efficiencies. At the beginning of the growing season, needles exposed to heat stress showed significantly higher basal fluorescence and lower quantum yield, performance index, critical temperature thresholds of PSII inactivation and non-photochemical yield in comparison to other months. The overall thermostability (heat-resistance) of PSII peaked in July and August, reflected in the lowest basal fluorescence and the highest quantum yield of PSII, critical temperature thresholds and yield of non-photochemical quenching under heat stress. Additionally, the ratio between chlorophyll and carotenoids was the highest in August and had a positive impact on PSII thermostability. Moreover, the high-temperature intrinsic water use efficiency was significantly higher during July and August than in June. Results show that 15-year-old trees of Picea abies at 840 m a.s.l. exhibited acclimative seasonal responses of PSII thermostability and intrinsic water use efficiency during an exceptionally warm year. Our results suggest that mountainous P. abies at lower altitudes can acclimate their photosynthetic apparatus to higher temperatures during summer.
Air temperature and photoperiod play an important role in the seedling development for tropical forest species. Both variables are sensitive to climate, and so evaluating thermal and photoperiodic effects on seedling development is fundamental, especially for climate change studies. Methods to quantify thermal time and the energy required for plants to reach a development stage include air temperature and cardinal temperatures. The photoperiod will also affect physiological reactions of a plant and thus its development. Here we evaluated the six thermal time methods widely used to compute thermal requirement, and identified the influence of the photoperiod from the 2015 and 2016 growing seasons and 12 sowing dates in Itajubá, Minas Gerais state, Brazil, on seedling development of three native tropical forest species Psidium guajava L. (Myrtaceae), Citharexylum myrianthum Cham. (Verbenaceae), and Bixa orellana L. (Bixaceae). The method used to quantify thermal time influenced the analytical results of seedling development; the one that considered three cardinal temperatures and compared them with the mean air temperature (Method 5) performed better in computing thermal requirements. The influence of photoperiod on seedling development was inconclusive for the three species, but all three developed better in mild temperatures (between 13.3 °C and 26.9 °C) with a photoperiod shorter than 13 h.
Germination at low spring temperatures may offer a competitive advantage for the growth and survival of plant species inhabiting temperate forest ecosystems. Pinus koraiensis is a dominant species in temperate forests of northeastern China. Its seeds exhibit primary morphophysiological dormancy following dispersal in autumn, limiting natural or artificial regeneration: direct seeding and planting seedlings in spring. The aim of this study was to determine the optimum cold stratification temperature that induces germination to increase towards lower temperatures. Seeds from two populations (Changbaishan and Liangshui) were cold stratified at 0, 5 and 10 °C. Germination to incubation temperatures (10/5, 20/10, 25/15 and 30/20 °C; 14/10 h day/night) were determined after 2 and 4 weeks, and 5.5 and 6.5 months of cold stratification. After 5.5 months, approximately 68–91% of seeds from both populations germinated at incubation temperatures of 25/15 °C and 30/20 °C, regardless of cold stratification temperatures. When the cold stratification temperature was reduced to 0 °C and the period increased to 6.5 months, germination at 10/5 °C significantly improved, reaching 37% and 64% for the Changbaishan and Liangshui populations, respectively. After 6.5 months of cold stratification, there was a significant linear regression between cold stratification temperatures and germination at 10/5 °C. The range in temperatures allowing for germination gradually expanded to include lower temperatures with decreasing cold stratification temperatures from 10 to 5 °C and further to 0 °C.
Old-growth forests play a key-role in reducing atmospheric carbon dioxide (CO2) concentrations by storing large CO2 amounts in biomass and soil over time. This quantifies the carbon pool into different forest compartments in three Mediterranean old-growth forests of Southern Italy populated by Pinus laricio, Fagus sylvatica and Abies alba. Ecosystem carbon pools have been assessed per compartment, i.e., living trees, deadwood, litterfall (foliar and woody), roots and 0–20 cm topsoil, combining the whole old-growth forest mass, (i.e., using tree allometric relationships, deadwood factor conversions, root-to-shoot ratios, litterfall and soil samplings) by the respective organic carbon concentrations. The results show the considerable capacity of these forest ecosystems in storing CO2 in biomass and soil, with carbon pool values ranging from 532.2 to 596.5 Mg C ha−1. Living trees and 0–20 cm topsoil had larger carbon pool, contributing 53.0 and 22.1%, respectively. In most cases, organic carbon concentration was higher (more than 60%) than the average carbon conversion rate of 50%, especially in living trees, deadwood, and woody litterfall. This study contributes further scientific evidence of the capacity of old-growth forests in storing CO2 in their different compartments, with special evidence on tree biomass, litterfall and mineral soil, thereby highlighting the key role of old-growth forests within the challenge of climate change mitigation.
Eucalyptus harvest residues are attractive energy production resources for the forestry industry. However, their removal can have adverse impacts on soil quality and forest productivity, especially in sandy soils. In this study, we assessed the effects of Eucalyptus harvest residue managements with variable intensity on forest productivity and on physical, chemical, and biological indicators of the soil quality. The experiment was conducted in a Quartzipsamment (33 g kg−1 clay) planted with Eucalyptus saligna in Barra do Ribeiro in southern Brazil. Before the Eucalyptus was planted, residues from the previous rotation were subjected to five different management treatments: (1) FRM, in which all forest residues (bark, branches, leaves, and litter) were allowed to remain on the soil and only trunk wood was removed; (2) FRMB, in which was identical to FRM except that bark was also removed; (3) FRMBr, in which only trunk wood and branches were removed; (4) FRR, which involved removing all types of residues (bark, branches, leaves, and litter); and, (5) FRRs, in which all forest residues from the previous rotation were removed, and leaves and branches from the new plantation were prevented from falling onto the soil surface using a shade net. Six years after planting, soil samples were collected at four different depths (0–2.5, 2.5–5, 5–10, and 10–20 cm) to determine 17 soil chemical, physical, and biological indicators. The results were combined into a soil quality index (SQI) using the principal component analysis approach. The SQI reduced by 30%, in the 0–20 cm layer, due to removal of harvest residues from the previous rotation, and collection of litter before it falls on the ground. The main drivers of SQI reduction were the principal components associated with soil organic matter and biological activity. Furthermore, the SQI was positively linearly related to tree height at P < 0.01 and to tree diameter at breast height at P = 0.07. The adverse impact on soil quality and forest productivity in our study indicates that removal of Eucalyptus harvest residues from sandy soils should be avoided.
Global climate changes have increased temperatures, radiation indexes, and consequently, irregularities in rainfall in mainly tropical countries, considerably hindering plant establishment in recovering degraded areas. The objective of this study was to evaluate the growth and physiological characteristics of one species of each successional group: pioneer, secondary, and climax when subjected to different light intensities and hydrogel as a soil conditioner during rainy and dry periods. The experiment was conducted in the ecotone between Brazil’s two largest biomes, the Cerrado and the Amazon in the State of Maranhão. The parameters consisted of three species: Guazuma ulmifolia Lam. (pioneer), Astronium fraxinifolium Schott (secondary), and Cariniana rubra Gardner ex Miers (climax). There were two light intensities: 70% and 100%, and two planting conditions: with and without soil conditioner (hydrogel). Gas exchanges were higher during the rainy season; the pioneer and secondary species had greater heights and photosynthetic rates in the dry period; the climax species had the lowest gas exchange and lowest recovery as rainfall resumed. The pioneer and secondary species showed higher physiological plasticity, denoting better adaption to environments with high irradiance. Hydrogel improved the photosynthetic performance of these species in the dry season and in areas with 100% sunlight.
Nitrogen (N) monitoring is essential in nurseries to ensure the production of high-quality seedlings. Near-infrared spectroscopy (NIRS) is an instantaneous, nondestructive method to monitor N. Spectral data such as NIRS can also provide the basis for developing a new vegetation spectral index (VSI). Here, we evaluated whether NIRS combined with statistical modeling can accurately detect early variations in N concentration in leaves of young plants of Annona emarginata and developed a new VSI for this task. Plants were grown in a hydroponics system with 0, 2.75, 5.5 or 11 mM N for 45 days. Then we measured gas exchange, chlorophylla fluorescence, and pigments in leaves; analyzed complete leaf nutrients, and recorded spectral data for leaves at 966 to 1685 nm using NIRS. With a statistical learning approach, the dimensionality of the spectral data was reduced, then models were generated using two classes (N deficiency, N) or four classes (0, 2.75, 5.5, 11 mM N). The best combination of techniques for dimensionality reduction and classification, respectively, was stepwise regression (PROC STEPDISC) and linear discriminant function. It was possible to detect N deficiency in seedlings leaves with 100% precision, and the four N concentrations with 93.55% accuracy before photosynthetic damage to the plant occurred. Thereby, NIRS combined with statistical modeling of multidimensional data is effective for detecting N variations in seedlings leaves of A. emarginata.
Cover crops have long been proposed as an alternative soil management for minimizing erosion rates in olive stands while providing additional ecosystem services. However, the trade-off between these benefits and the competition for water with the trees makes the definition of optimal management practices a challenging task in semiarid climates. This work presents an improved version of OliveCan, a process-based simulation model of olive orchards that now can simulate the main impacts of cover crops on the water and carbon balances of olive orchards. Albeit simple in its formulation, the new model components were developed to deal with different cover crop management strategies. Examples are presented for simulation runs of a traditional olive orchard in the conditions of southern Spain, evaluating the effects of different widths for the strip occupied by the cover crop (F cc) and two contrasting mowing dates. Results revealed that high F cc resulted in lower olive yields, but only when mowing was applied at the end of spring. In this regard, late mowing and high F cc was associated with lower soil water content from spring to summer, coinciding with olive flowering and the earlier stages of fruit growth. F cc was also negatively correlated with surface runoff irrespective of the mowing date. On the other hand, net ecosystem productivity (NEP) was substantially affected by both F cc and mowing date. Further simulations under future climate scenarios comparing the same management alternatives are also presented, showing substantial yield reductions by the end of the century and minor or negligible changes in NEP and seasonal runoff.
