Jezeera, A. | bioRxiv Science

bioRxiv2021

Quantitative estimates of deciduousness in woody species from a seasonally dry tropical forest are related to leaf functional traits and the timing of leaf flush

Leaf phenology based classification of woody species into discrete evergreen and deciduous categories is widely used in ecology, but these categories hide important variation in leaf phenological behaviour. Few studies have examined the continuous nature of deciduousness and our understanding of variation in quantitative estimates of leaf shedding behaviour and the causes and consequences of this is limited. In this study we monitored leaf phenology in 75 woody species from a seasonally dry tropical forest to quantify three quantitative measures of deciduousness, namely: maximum canopy loss, duration of deciduousness, and average canopy loss. Based on proposed drought tolerance and drought avoidance strategies of evergreen and deciduous species, respectively, we tested whether the quantitative measures of deciduousness were related to leaf functional traits. Additionally, to understand the functional consequences of variation in deciduousness we examined relationships with the timing of leaf flushing and senescing. We found wide and continuous variation in quantitative measures of deciduousness in these coexisting species. Variation in deciduousness was related to leaf function traits, and the timing of leaf flushing. Along a continuous axis ranging from evergreen to deciduous species, increasing deciduousness was associated with more acquisitive leaf functional traits, with lower leaf mass per area and leaf dry matter content, and greater leaf nitrogen content. These results indicate that the continuous nature of deciduousness is an important component of resource acquisition strategies in woody species from seasonally dry forests.

ecology↗

bioRxiv2020

Response of whole plant water use to limiting light and water conditions are independent of each other in seedlings of seasonally dry tropical forests

How co-occurring species vary in the utilization of a shared and limited supply of water, especially in the context of other limiting resources like light, is essential for understanding processes that facilitate species coexistence and community assembly. For seedlings in a seasonally dry tropical forest that experience large heterogeny in light and water conditions, how water use, leaf physiology, and subsequently plant growth, is affected by limited water and light availability is still not well understood. In a controlled common garden experiment with four co-existing and commonly occurring dry tropical forest species, we examined how whole plant water uptake, responds to limiting water and light conditions and whether these responses are reflected in leaf physiology, and translated to growth. Water use varied dramatically in seedlings of the four species with a five-fold difference in well-watered plants grown in full sunlight. Species varied in their response to shade, but did not differ in responses to the low water treatment, possibly resulting from the strong selective force imposed by the very low water availability and the long dry period characteristic of these seasonally dry forests. Interestingly, species responses in water use, physiology, and growth in limiting water conditions were independent of light. Thus, species response to both these limiting conditions may evolve independently of each other. Responses in water use were largely congruent with responses in leaf physiology and growth. However, while magnitude of changes in leaf physiology were largely driven by light conditions, changes in whole plant water use and growth were influenced to a greater degree by the water treatment. This highlights the need to measure whole plant water use to better understand plant growth responses in these seasonally dry tropical forests.

ecology↗