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We investigated how differences in mangrove island micro-elevation (i.e., habitat, center vs. edge) affect tree physiology in a scrub mangrove forests of the southeastern Everglades. We measured leaf gas exchange rates of scrub Rhizophora mangle L. trees monthly during 2019, hypothesizing that CO2 assimilation (Anet) and stomatal conductance (gsw) would decline with increasing water levels and salinity, expecting more-considerable differences at mangrove-island edges than centers, where physiological stress is greatest. Water levels varied between 0 and 60 cm from the soil surface, rising during the wet season (May-October) relative to the dry season (November-April). Porewater salinity ranged from 15 to 30 ppt, being higher at mangrove-island edges than centers. Anet maximized at 15.1 μmol m-2 s-1, and gsw was typically -2 s-1, both of which were greater in the dry than the wet season and greater at island centers than edges, with seasonal variability being roughly equal to variation between habitats. After accounting for season and habitat, water level positively affected Anet in both seasons but did not affect gsw. Similarly, porewater salinity had a slightly positive marginal effect on Anet but a negligible effect on gsw. Our findings suggest that inundation stress (i.e., water level) is the primary driver of variation in leaf gas exchange rates of scrub mangroves in the Florida Everglades, while also constraining Anet more than gsw. The interaction between inundation stress due to permanent flooding and habitat varies with season as physiological stress is alleviated at higher-elevation mangrove-island center habitats during the dry season. Freshwater inflows during the wet season, increase water levels and inundation stress at higher-elevation mangrove-island centers, but also potentially alleviate salt and sulfide stress in soils. Thus, habitat heterogeneity leads to differences in nutrient and water acquisition and use between trees growing in island centers versus edges, creating distinct physiological controls on photosynthesis, which likely affect carbon flux dynamics of scrub mangroves in the Everglades.

For plants, elemental nutrients are important belowground resources that sustain growth and survival. To understand how tropical plant nutrient status responds to environmental variation, we asked whether concentrations of nutrients in root and leaf tissues track gradients in soil nutrient concentrations and if tissue nutrient concentrations respond independently or in concert to soil nutrient concentrations. We measured soil nutrient concentrations of rhizosphere soil and root and leaf tissue elemental concentrations of saplings from 14 Angiosperm families in montane tropical forest of Jianfengling, China. Using mixed-effects models, we modeled the nutrient concentration of plant tissues as a function of soil resources. Of fourteen elements measured, seven —nitrogen, boron, phosphorus, potassium, manganese, copper and zinc— increased in concentrations in root and leaf tissues with higher soil nutrient availability; two decreased —aluminum and carbon; three were invariant —magnesium, sulfur, and calcium; and two —sodium and iron— showed contrasting patterns between leaves and roots. Eight elements necessary to leaf physiological function, but also used in root functioning —nitrogen, boron, magnesium phosphorus, sulfur, potassium, calcium, manganese— were more concentrated in leaves than roots. Additionally, most elements showed tradeoffs in concentrations between roots and leaves. Plant lineage (i.e. family) explained very little of the variation about this overall trend. Overall, increases in tissue nutrient concentrations with soil fertility were subtle if present at all. Thus, we conclude that tissue nutrients of juvenile tropical trees have a high degree of elemental homeostasis with local-scale soil nutrient content in Jianfengling.

Linking drought to the timing of physiological processes governing tree growth remains one limitation in forecasting climate change effects on tropical trees. Using dendrometers, we measured fine-scale growth for 96 trees of 25 species from 2013 to 2016 in an everwet forest in Puerto Rico. Rainfall over this time span varied, including an unusual, severe El Niño drought in 2015. We assessed how growing season onset, median day, conclusion, and length varied with absolute growth rate and tree size over time. Stem growth was seasonal, beginning in February, peaking in July, and ending in November. Species growth rates varied between 0 and 8 mm/year and correlated weakly with specific leaf area, leaf phosphorus, and leaf nitrogen, and to a lesser degree with wood specific gravity and plant height. Drought and tree growth were decoupled, and drought lengthened and increased variation in growing season length. During the 2015 drought, many trees terminated growth early but did not necessarily grow less. In the year following drought, trees grew more over a shorter growing season, with many smaller trees showing a post-drought increase in growth. We attribute the increased growth of smaller trees to release from light limitation as the canopy thinned because of the drought, and less inferred hydraulic stress than larger trees during drought. Soil type accounted for interannual and interspecific differences, with the finest Zarzal clays reducing tree growth. We conclude that drought affects the phenological timing of tree growth and favors the post-drought growth of smaller, sub-canopy trees in this everwet forest.

We investigated the relative and combined effect of topography and light environment on the recruitment of seedlings in a subtropical forest after snow damage to the canopy. The tree seedling community in an old-growth subtropical forest was monitored using 500 2 m × 2 m seedling plots at six-month intervals for 2 years. With a focus on recruitment following canopy damage, we related abiotic and biotic environmental variables to seedling dynamics, and we tested if significant topographic and light habitat associations were present for seedlings recruiting via a torus translation test. Then, we used variance partitioning to examine the relative effects of spatial, topographic and light variables on the temporal assemblages of seedlings. A total of 3047 seedlings from 58 species recruited in the first 2 years following snow damage. At the community level, increases in seedling abundance and richness were positively correlated with canopy openness and negatively correlated with elevation. At the species level, both pioneer and late-successional tree species had more recruits in high light environment than in low light environment. 84.3% of the recruiting seedlings were significantly associated to either light environment (35.7%), topography (26.5%) or both (22.1%). Despite this, at the plot level, spatial variables (PCNM) explained the majority of the variability in seedling composition over time. Our results suggest that snow damage to the canopy increases species richness and abundance via light-facilitated seedling recruitment, and that the composition of recruiting seedlings was largely spatially dependent. Topographic habitat filtering acts as a persistent force in determining the recruitment of seedlings and increases in strength with increased light-facilitated seedling recruitment. Our results highlight that, in this subtropical forest, both light requirement and topographic specialization interact over time to play a key role in promoting coexistence of tree species through selection of individuals at the seedling stage. We also suggest exploring the possibilities of management intervention to speed up the recovery of this forest.

Accounting for intraspecific trait variation (ITV) is central to plant ecology and crucial for vegetation modeling efforts. ITV can be substantial; however, it remains unclear how ITV influences community-weighted mean (CWM) trait estimates. We use leaf and root trait data from 423 trees of 72 species from 15 Angiosperm families in combination with community data from 164 small plots comprising 582 species to evaluate the contribution of ITV to CWMs, comparing unlogged, primary forest to selectively-logged and clear-cut secondary forest. We examine the effect of gap-filling missing trait values via phylogenetic generalized linear modeling (PhyloPars) on CWMs. For six of seven traits, ITV negatively covaried with species turnover to generate larger CWM differences than observed if ITV was not integrated. For example, plot average CWM specific leaf area was 10.7 and 10.4 m2 kg− 1 for primary and secondary forest, not accounting for ITV, but shifted to 9.8 and 11.1 m2 kg− 1 after doing so. Specific root length showed a similar trend. Our results from 72-species assemblages were supported by the results from the gap-filled analysis using the entire community, where the contribution of ITV to CWMs ranged from 25 to 75%, with nearly all trait variation due to forest type attributable to ITV. Therefore, CWM trait estimates became more-conservative with forest age, whereas ITV for many traits showed an acquisitive shift, and because of negative covariation between ITV and species turnover, forest age-related CWM differences increased. Differences were unaffected, if not strengthened, by gap-filling incomplete functional trait matrices.

Legumes provide an essential service to ecosystems by capturing nitrogen from the atmosphere and delivering it to the soil, where it may then be available to other plants. However, this facilitation by legumes has not been widely studied in global tropical forests. Demographic data from 11 large forest plots (16–60 ha) ranging from 5.25° S to 29.25° N latitude show that within forests, leguminous trees have a larger effect on neighbor diversity than non-legumes. Where soil nitrogen is high, most legume species have higher neighbor diversity than non-legumes. Where soil nitrogen is low, most legumes have lower neighbor diversity than non-legumes. No facilitation effect on neighbor basal area was observed in either high or low soil N conditions. The legume–soil nitrogen positive feedback that promotes tree diversity has both theoretical implications for understanding species coexistence in diverse forests, and practical implications for the utilization of legumes in forest restoration., Xu et al. examine the effect of leguminous trees on neighbor diversity across 11 plots in tropical forests around the world, and find that in high soil nitrogen conditions, most legume species have higher neighbor diversity than non-legumes, and vice versa where soil nitrogen is low. Their results have practical implications for the utilization of legumes in forest restoration.

The hardwood forests of south Florida, commonly referred to as hammocks, persist as well‐drained patches of broadleaf forest, embedded in a matrix of brackish water swamp, freshwater marsh, or pineland. Little is known about the patterns of community assembly of these subtropical forest communities in the landscape mosaic of south Florida. We used a functional trait approach to understand the composition of these communities and their responses to environmental variation across four areas of south Florida: the pine rocklands and freshwater marshes in Everglades National Park, and the lower and upper Florida Keys, where the hammocks are surrounded by halophytic swamp communities. These sites represent an environmental gradient from less‐productive, more xeric sites in the lower Florida Keys, to more‐productive, wetter sites in the Everglades marshes. We examined the patterns of trait variation at three levels (individual, population, and community) to examine the underlying processes driving assembly in these hammock communities. To understand processes governing community composition in each site, we used methods that partition variance in six traits (maximum tree height, specific leaf area, wood specific gravity, leaf nitrogen, leaf phosphorus, and leaf stable carbon isotope ratios) into internal and external filtering components. Community‐weighted mean trait values for three traits (specific leaf area, height, and leaf phosphorus) increased significantly from dry, less‐productive coastal sites in the Florida Keys to the moist, more‐productive areas on the mainland, while wood specific gravity and leaf δ13C showed the opposite pattern. For one or more traits per site, standardized effect sizes differed significantly from null expectation. Processes such as competition for resources (e.g., water, nutrients, light) and species sorting across microhabitats (i.e., within site) operate to increase local functional trait variation within communities and among species across sites. External filtering on individuals for height and leaf phosphorus differed significantly from null expectations across sites, while external filtering on species was only observed for specific leaf area, maximum tree height, and leaf phosphorus. These results are consistent with strong environmental filtering across the region, among local communities differing in freshwater accessibility or that occupy different positions along strong edaphic gradients. Our results confirm the importance of intraspecific variation among species and reflect a high degree of trait plasticity across the environmental gradient.

The tree growth and mortality trade-off is well documented and plays a key role in forests by forming the basis of many ecosystem processes and contributing to tree species coexistence. One area that requires further understanding is how the growth-mortality trade-off is influenced by biotic and abiotic interactions in the forest. In this study, we used a 5-year interval of tree growth and mortality demographic data from a 9-ha forest dynamics plot in a temperate old-growth Chinese forest to address two questions, (1) What is the nature of the growth-mortality trade-off among species in this forest? (2) Are there differences between the responses of tree growth and mortality to local neighborhood variables, both biotic and abiotic? Specifically, do these responses vary among species and with tree size? For the first question, we hypothesized that, within species, mortality rate would be negatively correlated with growth rate, whereas among species it would be positively correlated. For the second question, we expected biotic and abiotic factors to both be important for tree mortality; but expected biotic factors to be more important than abiotic factors for tree growth. The responses of tree growth and mortality to local neighborhood variables, both biotic and abiotic, varied among species. Abiotic factors were more important than biotic factors for small trees; biotic variables were stable with tree size for both small and large trees. Our results showed that there were differences between the responses of tree growth and mortality to local neighborhood variables (i.e., biotic and abiotic) in this temperate forest community. The responses of tree mortality to local neighborhood variables strongly varied across species. Abiotic factors were only important for the growth of small trees. Biotic factors were stable with tree size for growth of small and large trees, but not for mortality. Mortality was negatively correlated with growth for large trees within species; growth-mortality trade-off among species was found to be more accentuated for small trees. The responses of tree mortality to local neighborhood variables differed strongly across species, whereas the responses of tree growth to local neighborhood variables varied among size classes. Tree growth and mortality is tightly correlated both within (negatively) and among species (positively), and their relationships are both size dependent in this temperate forest. Our findings highlight that differential responses of tree growth and mortality to local neighborhood variables continue to shape the forest community well after sapling establishment in this temperate forest community.

Mangrove forests growing at the poleward edges of their geographic distribution are occasionally subject to freezing (&lt, 0 °C) and cold wave (&gt, 0 °C) events. Cold wave effects on mangrove trees are well documented and adaptation to cold stress has been reported for local mangrove populations in the North Atlantic. However, there is less understanding of effects of cold waves on mangroves in the northern Pacific, especially at the regional scale. Moreover, it is unclear if cold tolerant mangrove species of North Asia display variation in resistance to cold temperatures across their geographic distribution. Using a cold wave event that occurred in January 2021, we evaluated the effects of low temperatures on vegetation index (VI) change (relative to a recent five-year baseline) for mangrove forests dominated by Kandelia obovata (Rhizophoraceae) and Avicennia marina (Acanthaceaee) at the northern edge of their geographical range. We used two VIs derived from Sentinel-2 imagery as indicators for canopy health: the normalized difference infrared index (NDII) and the chlorophyll red-edge index (ChlRE), which reflect forest canopy water content and chlorophyll concentration, respectively. We isolated the cold wave effects on the forest canopy from phenology (i.e., cold wave induced deviation from a five-year baseline) and used multiple linear regression to identify significant climatic predictors for the response of mangrove forest canopy VI change to low temperatures. For areas where the cold wave resulted in temperatures &lt, 10 °C, immediate decreases in both VIs were observed, and the VI difference relative to the baseline was generally greater at 30-days after the cold wave than when temperatures initially recovered to baseline values, showing a slight delay in VI response to cold wave-induced canopy damage. Furthermore, the two VIs did not respond consistently suggesting that cold-temperature induced changes in mangrove canopy chlorophyll and water content are affected independently or subject to differing physiological controls. Our results confirm that local baseline (i.e., recent past) climate predicts canopy resistance to cold wave damage across K. obovata stands in the northern Pacific, and in congruence with findings from New World mangroves, they imply geographic variation in mangrove leaf physiological resistance to cold for Northern Pacific mangroves.

Understanding the ecological processes that regulate microbial community assembly in different habitats is critical to predict microbial responses to anthropogenic disturbances and environmental changes. Rubber (Hevea brasiliensis) and Eucalypt (Eucalyptus urophylla) plantations (thereafter RP and EP) are rapidly established at the expense of forests in tropical China, greatly affecting tropical soils and their processes. However, the assembly processes of soil microbial communities after forest conversions remain unclear. We investigated soil microbial communities&rsquo, attributes and quantified the portion of deterministic assembly variation in two RP (a 3- and a 5-year-old) and two EP (a 2- and a 4-year-old) in Southern China. Shannon and Faith&rsquo, s Phylogenetic &alpha, diversity of both bacterial and fungal communities were higher in RP than in EP, regardless of plantation age or soil depth (0&ndash, 50 cm). Bacterial and fungal community structure was significantly different among the four plantations. The dominant microbial taxa in RP closely tracked the availability of nitrogen, phosphorus and potassium (K) while those in EP were closely related to the high total K content. Microbial co-occurrence networks in RP were more modular than those in EP, as governed by more keystone taxa that were strongly dependent on soil available nutrients. Environmental filtering imposed by soil nutrients heterogeneity contributed a considerable portion (33&ndash, 47%) of bacterial assembly variation in RP, but much less (8&ndash, 14%) in EP. The relative contribution of environmental selection on fungal assembly was also greater in RP than in EP. Our findings suggest that in RP clear microbial community patterns exist with respect to soil nutrients, whereas in EP microbial community assembly patterns are more stochastic and variable. The large variation in soil microbial community assembly patterns in EP could lead to fragile and unstable microbial-soil relationships, which may be one factor driving soil degradation in EP.