ORCID Profile
0000-0001-5637-3015
Current Organisation
The University of Maine
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Publisher: Wiley
Date: 18-08-2021
DOI: 10.1111/ELE.13856
Abstract: Hydraulic failure caused by severe drought contributes to aboveground dieback and whole‐plant death. The extent to which dieback or whole‐plant death can be predicted by plant hydraulic traits has rarely been tested among species with different leaf habits and/or growth forms. We investigated 19 hydraulic traits in 40 woody species in a tropical savanna and their potential correlations with drought response during an extreme drought event during the El Niño–Southern Oscillation in 2015. Plant hydraulic trait variation was partitioned substantially by leaf habit but not growth form along a trade‐off axis between traits that support drought tolerance versus avoidance. Semi‐deciduous species and shrubs had the highest branch dieback and top‐kill (complete aboveground death) among the leaf habits or growth forms. Dieback and top‐kill were well explained by combining hydraulic traits with leaf habit and growth form, suggesting integrating life history traits with hydraulic traits will yield better predictions.
Publisher: Wiley
Date: 07-02-2023
DOI: 10.1111/NPH.18747
Abstract: Mistletoes play important roles in biogeochemical cycles. Although many studies have compared nutrient concentrations between mistletoes and their hosts, no general patterns have been found and the nutrient uptake mechanisms in mistletoes have not been fully resolved. To address the water and nutrient relations in mistletoes compared with their hosts, we measured 11 nutrient elements, two isotope ratios and two leaf morphological traits for 11 mistletoe and 104 host species from four sites across a large environmental gradient in southwest China. Mistletoes had significantly higher phosphorus, potassium, and boron concentrations, nitrogen isotope ratio, and lower carbon isotope ratio (δ 13 C) indicative of lower water‐use efficiency than hosts, but other elements were similar to those in hosts. Sites explained most of the variation in the multidimensional trait space. With increasing host nitrogen concentration, both mistletoe δ 13 C and the difference between mistletoe and host δ 13 C increased, providing evidence to support the ‘nitrogen parasitism hypothesis’. Host nutrient concentrations were the best predictors for that of the mistletoe nutrient elements in most cases. Our results highlight the important roles of environmental conditions and host nutrient status in determining mistletoe nutrient pools, which together explain their trophic interactions with hosts in subtropical and tropical ecosystems.
Publisher: Wiley
Date: 06-01-2023
DOI: 10.1111/PCE.14524
Abstract: Within vascular plants, the partitioning of hydraulic resistance along the soil‐to‐leaf continuum affects transpiration and its response to environmental conditions. In trees, the fractional contribution of leaf hydraulic resistance (R leaf ) to total soil‐to‐leaf hydraulic resistance (R total ), or fR leaf (=R leaf /R total ), is thought to be large, but this has not been tested comprehensively. We compiled a multibiome data set of fR leaf using new and previously published measurements of pressure differences within trees in situ. Across 80 s les, fR leaf averaged 0.51 (95% confidence interval [CI] = 0.46−0.57) and it declined with tree height. We also used the allometric relationship between field‐based measurements of soil‐to‐leaf hydraulic conductance and laboratory‐based measurements of leaf hydraulic conductance to compute the average fR leaf for 19 tree s les, which was 0.40 (95% CI = 0.29−0.56). The in situ technique produces a more accurate descriptor of fR leaf because it accounts for dynamic leaf hydraulic conductance. Both approaches demonstrate the outsized role of leaves in controlling tree hydrodynamics. A larger fR leaf may help stems from loss of hydraulic conductance. Thus, the decline in fR leaf with tree height would contribute to greater drought vulnerability in taller trees and potentially to their observed disproportionate drought mortality.
Publisher: MDPI AG
Date: 19-03-2021
DOI: 10.3390/W13060850
Abstract: Mangroves growing in tropical and subtropical intertidal zones face challenges from warming and altered rainfall patterns associated with global climate change. Intraspecific variation in hydraulic traits may allow a mangrove species to acclimate to novel climatic conditions, yet little is known regarding the potential for adaptive plasticity in these traits. In this study, we aimed to quantify the variation in plant hydraulic traits of two widespread mangrove species growing across a latitudinal gradient. We investigated the xylem hydraulic structure and function of Avicennia marina and Aegiceras corniculatum, across three sites spanning a latitudinal gradient of 17.45° in eastern Australia. We found that both species were highly resistant to xylem embolism and that there was significant intraspecific variation in hydraulic traits between sites. The highest embolism resistance and sapwood-specific hydraulic conductivity (KS) were found at the lowest latitude site that had the highest mean annual temperature and precipitation. A. marina showed no differences in vessel size and density among sites. It has other special features such as successive cambia enhancing its ability to adapt to a large environmental gradient. In contrast, A. corniculatum showed higher vessel densities at lower latitudes. There was a significant and positive correlation (R2 = 0.72, p 0.05) between KS and embolism resistance across species and sites, suggesting the absence of a tradeoff between hydraulic efficiency and safety. Both embolism resistance and KS were negatively correlated with wood density but positively with vessel wall reinforcement. This study reveals that these two widespread mangrove species were adapted to warmer climates by enhancing both hydraulic efficiency and safety.
Publisher: MDPI AG
Date: 29-11-2021
DOI: 10.3390/F12121655
Abstract: Tropical forests play important roles in global carbon cycling. Tree-ring analysis can provide important information for understanding long-term trends in carbon-fixation capacity under climate change. However, tree-ring studies in tropical regions are limited. We carried out a tree-ring analysis to investigate the dendrochronological potential of the tropical forest tree Choerospondias axillaris (Anacardiaceae) in east-central Thailand. Our study focused on growth-climate relationships and long-term growth trends. A chronology was constructed covering the period from 1932 to 2019. The tree-ring width index of C.axillaris was positively correlated with precipitation in June, July, and October. Furthermore, growth of C.axillaris was positively correlated with the Standardized Precipitation-Evapotranspiration Index (SPEI) from July to October, indicating that growth of C.axillaris is mainly limited by moisture availability in the late monsoon season. Moving correlation analysis further revealed the consistency and temporal stability of the relationship of tree growth with monsoon season precipitation and SPEI during the period under study. There was a significant increasing trend in long-term growth from 1932 to 2002 (slope = 0.017, p 0.001) however, long-term growth decreased from 2003 to 2019 (slope = −0.014, p 0.001). Our study provides important insight into the growth-climate correlations of a broad-leaved tree species in a dry evergreen forest in tropical Asia.
No related grants have been discovered for Yongjiang Zhang.