Friend or foe? The role of biotic agents in drought-induced plant mortality

Abstract

Plant mortality is a complex process influenced by both biotic and abiotic factors. In recent decades, widespread mortality events have been attributed to increasing drought severity, which has motivated research to examine the physiological mechanisms of drought-induced mortality, particularly hydraulic failure. Drought-based mortality mechanisms are further influenced by plant interactions with biota such as neighboring plants, insect pests, and microbes. In this review, we highlight some of the most influential papers addressing these biotic interactions and their influence on plant mortality. Plant-plant interactions can be positive (facilitation), neutral, or negative (competition), depending on drought intensity and neighbor identity. For example, standscale mortality likely increases with basal area (an index of competition). However, the diversity of forest stands matters, as more diverse forests suffer less mortality from drought than species-poor forests. Dense forest stands also increase bark beetle attack frequency, which can exacerbate drought stress and mortality, particularly for fast-growing species with lower defense allocation. In some cases, however, drought stress can alleviate biotic attack, depending on feedbacks between plant and pest physiology. Finally, plant interactions with beneficial microorganisms can increase drought tolerance, reduce the likelihood of mortality, and even extend plant distributions into drier habitats. Our review suggests more work is needed in natural herbaceous plant communities as well as dry tropical ecosystems where mortality mechanisms are less understood. Overall, relatively few studies directly link biotic interactions with the physiological mechanisms of mortality. Simultaneous manipulations of biotic interactions and measurements of physiological thresholds (e.g., xylem cavitation) are needed to fully represent biotic interactions in predictive models of plant mortality.

Drought survival and recovery in grasses: Stress intensity and plant–plant interactions impact plant dehydration tolerance

“…We show that plant-plant interactions create an additional source of variation in plant dehydration tolerance (χ² = 8.87, p = 0.0118, Table 1) that has been rarely tested previously (Griffin-Nolan et al, 2021). As expected, we found opposite responses between the two species, suggesting a positive relationship between plant dehydration tolerance and benefits from biodiversity effects in mixtures.…”

“…Despite changes in plant density, we support that plant diversity improves the resilience capacity to drought in grass mixtures (Tilman & Downing, 1994), as found in forests (Grossiord et al, 2014; Hisano et al, 2019). This effect could be even higher when complementary drought strategies are associated together and allow recovering productivity after drought (Wright et al, 2021), for example, in natura where F. arundinacea can efficiently better ‘avoid’ dehydration by capturing water from deep soil layers, reducing interspecific competition and maximizing ecosystem functioning (Godoy et al, 2020).…”

“…Furthermore, biodiversity is increasingly recognized to buffer plant communities against the negative impacts of climate extremes (Isbell et al, 2017;Loreau et al, 2021) like drought (Wagg et al, 2017;Wright et al, 2021) due to positive plant-plant interactions (e.g., facilitation) and complementarity effects among plants (e.g., niche difference), which together have a potentially positive effect (i) on plant survival during drought and (ii) on plant recovery after the drought (Haberstroh et al, 2021). However, few studies have assessed how positive or negative interactions between neighbouring plants directly affect plant dehydration tolerance, drought survival and drought recovery (Griffin-Nolan et al, 2021).…”

Field experiments have enhanced our understanding of drought impacts on terrestrial ecosystems—But where do we go from here?

“…McDowell et al, 2008McDowell et al, , 2022Peltier et al, 2023), much less is known about mortality mechanisms in herbaceous-dominated ecosystems (e.g. Griffin-Nolan et al, 2021;Niu et al, 2014;Norton et al, 2016). This is a critical knowledge inequity because herbaceous-dominated ecosystems may equal or exceed the global land cover of forests.…”

Root Carbon Resources Determine Survival and Growth of Young Trees Under Long Drought in Combination With Fertilization

“…Similar to results gained from most drought intensity experiments with trees (Li et al, 2013;Schönbeck et al, 2018Schönbeck et al, , 2020aZhang et al, 2020;Ouyang et al, 2021), the present study found that the longer drought duration treatments (D2, D3) did not decrease the end-season leaf NSC (pre-winter) levels (Figures 3A,F), although the D2 and D3 treatment significantly decreased leaf photosynthesis of the two species (Figures 2C-F). This might be explained by the osmoregulation strategy of plants suffering from drought stress on the one hand (O'Brien et al, 2014;Dickman et al, 2015), and on the other hand, it may be a result of basipetal carbon translocation failure (Rowland et al, 2015), if the phloem function becomes impaired and carbon translocation gets limited or stopped by hydraulic failure caused by severe or long drought stress (Griffin-Nolan et al, 2021). In this case, lower NSC levels in the sink tissues of shoots, and especially roots, and thus carbon limitation may be expected.…”