Mon, Aug 15, 2022: 2:00 PM-2:15 PM
518B
Background/Question/MethodsAs the climate continues to change, understanding the relative importance of abiotic conditions versus biotic interactions for plant performance in natural systems is critical. However, the direct effects of climate change versus those mediated by biotic interactions are currently difficult to predict. We investigated how water availability, plant-plant interactions, and natural variation in overstory cover and soil properties influenced vital rates within a diverse community of annual plants in semi-arid south-west Western Australia. We sowed seeds of nine focal species into blocks of ‘sun’ and ‘shade’ across a reserve, removed all neighbouring plants from half of the interaction neighbourhoods, and used rainout shelters to either reduce rainfall by 50% or increase rainfall by 50% (by redistributing the intercepted rainfall) relative to ambient plots. We examined the relative importance of abiotic and biotic factors for survival and fecundity and tested whether leaf-level species’ functional traits (specific leaf area, leaf dry matter content, and carbon isotope discrimination) explained these responses.
Results/ConclusionsFor 6 of 9 species, germination was higher in more open, less fertile plots. Of 1400 focal individuals, 609 survived to produce seeds (44%). Abiotic and biotic factors were similarly important for survival, however abiotic factors were relatively more important for fecundity. Competition from neighbours significantly reduced survival of three focal species, and water addition and soil pH had significantly positive effects on the survival of two species. In fecundity models, neighbouring plants reduced seed production for only one species, whereas soil pH, overstory cover and soil fertility had positive effects for four species. For two species, conditions that were favourable for germination were unfavourable for fecundity. Measured functional traits did not modulate survival responses to any abiotic or biotic factor. However, specific leaf area explained the response of fecundity to the abiotic environment (soil pH, overstory cover and soil fertility). Overall, plant-plant interactions were as important as abiotic conditions for survival, but not for fecundity. We provide much-needed empirical evidence of species' differential responses to abiotic and biotic conditions, including counteracting responses of different vital rates to the same conditions. This highlights the importance of measuring more than one vital rate as a fitness proxy.
Results/ConclusionsFor 6 of 9 species, germination was higher in more open, less fertile plots. Of 1400 focal individuals, 609 survived to produce seeds (44%). Abiotic and biotic factors were similarly important for survival, however abiotic factors were relatively more important for fecundity. Competition from neighbours significantly reduced survival of three focal species, and water addition and soil pH had significantly positive effects on the survival of two species. In fecundity models, neighbouring plants reduced seed production for only one species, whereas soil pH, overstory cover and soil fertility had positive effects for four species. For two species, conditions that were favourable for germination were unfavourable for fecundity. Measured functional traits did not modulate survival responses to any abiotic or biotic factor. However, specific leaf area explained the response of fecundity to the abiotic environment (soil pH, overstory cover and soil fertility). Overall, plant-plant interactions were as important as abiotic conditions for survival, but not for fecundity. We provide much-needed empirical evidence of species' differential responses to abiotic and biotic conditions, including counteracting responses of different vital rates to the same conditions. This highlights the importance of measuring more than one vital rate as a fitness proxy.