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Abstract

Vegetation is a highly dynamic component of the Earth surface and substantially alters the
water cycle. Particularly the process of oxygenic plant photosynthesis determines vegetation
connecting the water and carbon cycle and causing various interactions and feedbacks across
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Earth spheres. While vegetation impacts the water cycle, it reacts to changing water
availability via functional, biochemical and structural responses. Unravelling the resulting
complex feedbacks and interactions between the plant-water system and environmental
change is essential for any modelling approaches and predictions, but still insufficiently
understood due to currently missing observations. We hypothesize that an appropriate crossscale
monitoring of plant-water relations can be achieved by combined observational and
modelling approaches. This paper reviews suitable remote sensing approaches to assess plantwater
relations ranging from pure observational to combined observational-modelling
approaches. We use a combined energy balance and radiative transfer model to assess the
explanatory power of pure observational approaches focussing on plant parameters to estimate
plant-water relations, followed by an outline for a more effective use of remote sensing by
their integration into soil-plant-atmosphere continuum (SPAC) models. We apply a
mechanistic model simulating water movement in the SPAC to reveal insight into the
complexity of relations between soil, plant and atmospheric parameters, and thus plant-water
relations. We conclude that future research should focus on strategies combining observations
and mechanistic modelling to advance our knowledge on the interplay between the plantwater
system and environmental change, e.g. through plant transpiration.