The degree to which forests provide ecosystem services in the wake of global change depends, in part, on how they cope with novel or enhanced stressors like drought. Plants have been found to alter their morphology, physiology, as well as utilize their mutualisms with soil and plant microbes to help tolerate drought conditions. The emerging research on tree drought tolerance has inspired my dissertation research which revolves around this topic.

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Chapter 1 (published in Oecologia): 

Soil microbes aid in the drought tolerance of plants, yet the extent to which a microbial community’s previous drought exposure can affect plant responses to contemporary drought is largely unknown. To address this gap using a greenhouse experiment, we planted saplings of three eastern hardwoods (Prunus virginiana, Liriodendron tulipifera, and Quercus rubra) in field soils exposed to experimentally-induced drought or ambient moisture. Then, we altered the watering regime of the pots to induce contemporary drought (or no water stress) and measured several physiological responses. In pots containing soils with no drought history, contemporary drought reduced C assimilation rates, stomatal conductance, and leaf water potential in all tree species, as expected. However, in pots containing soils with a drought history, one species – P. virginiana – was buffered from the effects of contemporary drought, displaying no drought-induced changes in physiology. The buffering effect of the soil drought history treatment also affected soluble sugars, which increased to a lesser degree (in response to contemporary drought) than in soils with no drought history. These effects were not apparent in the other two species. Sterilized soils suggest that the soil drought history effect on some physiological variables in P. virginiana likely resulted from drought-induced responses of soil microbes as opposed to soil physical or chemical changes. Collectively, our results indicate that in addition to plant hydraulic traits, the physiological responses of some tree species to drought may depend, in part, on plant-soil-microbe interactions shaped by past stress exposures.

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Chapter 2 (in prep):

Root traits are in part determined by environmental conditions, such as drought. However, recent literature suggests that root traits may not only be influenced by the abiotic environment, but they can also be influenced by soil microbes via their release of compounds such as plant-growth promoting hormones. Further, there are few if any studies investigating the influence of soil microbial history on root morphological traits under water stress. Thus, I ask: How does the drought legacy of soil microbes impact root traits under subsequent drought? By understanding how microbial drought legacies impact root traits, we can predict how future climatic conditions will impact our forests and their carbon cycling. 

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Chapter 3:

​The formation of soil organic matter (SOM), the largest reservoir of carbon in forests (Dixon et al. 1994), is highly dependent on dead tissue quality/chemistry (Cotrufo et al. 2015). Thus, it is important to connect how changes in tissue chemistry in response to drought impact the formation and stability of SOM. Additionally, changes in SOM have been found to alter soil water retention (Bucka et al. 2021). Therefore, tissue chemistry responses to historical drought may cause downstream changes in the soil water retention of the soil, modulating the severity of root-zone water depletion in contemporary droughts. By understanding how drought influences different SOM pools and soil water retention via changes in plant chemistry, I will be able to better predict how drought will impact long-term soil carbon storage and tree vulnerability to future drought.

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Principal Investigator- Richard Phillips, Ph.D.

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