Abstract
We investigated the impact of soil moisture on gross primary production (GPP), chlorophyll content, and canopy water content represented by remotely sensed vegetation indices (VIs) in an open grassland and an oak savanna in California. We found for the annual grassland that GPP late in the growing season was controlled by the declining soil moisture, but there was a 10–20-day lag in the response of GPP to soil moisture. However, during the early and middle part of the growing season, solar radiation accounted for most of the variation in GPP. In the oak savanna, the grass understory exhibited a similar response, but oak trees were not sensitive to soil moisture in the upper 50 cm of the soil profile. Furthermore, while we found most VIs to be more or less related to soil moisture, the Visible Atmospherically Resistance Index (VARI) was the most sensitive to the change of soil moisture.
Highlights
Plant-available soil moisture is a key element in ecosystem functioning, since it links energy balance and hydrological cycles, contributes to vegetation composition and richness, and impacts productivity
Remotely sensed vegetation indices together with surface radiant temperature have been used to estimate surface soil moisture [36,37,38]. These results provide evidence that vegetation indices are responsive to soil moisture variations in arid and semiarid areas, but the relationship between vegetation indices and soil moisture is modified by temperature and soil properties
To explore vegetation responses to changes in soil moisture, we evaluated the relationship between soil moisture and gross primary production (GPP), and remotely sensed measures of greenness and canopy water content in a Mediterraneanclimate annual grassland and an oak savanna
Summary
Plant-available soil moisture is a key element in ecosystem functioning, since it links energy balance and hydrological cycles, contributes to vegetation composition and richness, and impacts productivity. California’s Mediterranean climate is characterized by highly variable winter precipitation and prolonged summer drought, and its vegetation communities are strongly affected by the availability of water, resulting in pronounced annual cycles of growth and senescence [1]. Given the nature of the hydroclimate regime in California, understanding the response of different plant functional types to soil water availability should be a primary objective of any advanced natural resource management system. Spatial niche separation in root distributions appears to be more prevalent in arid systems [5], and plant-available moisture, rather than nutrients, may be the main resource limiting plant growth in savannas [6, 7]. The correlation between photosynthesis, chlorophyll content and canopy water content with soil moisture varies among
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