干旱区生态环境知识资源中心

Thermal dissipation of excess excitation energy is an important photoprotective mechanism that plants have evolved to cope with surplus illumination. However, light-energy-partitioning dynamics in an exotic sand-dune willow (Salix psammophila) commonly used in restoring and/or stabilizing sand lands in northwestern China is largely unknown. In this study, chlorophyll fluorescence (ChlF) of photosystem II (PSII) was continuously monitored in situ in Salix psammophila to investigate plant acclimation processes driven by excessive solar radiation and extreme air temperatures (T-a). As part of a heat-regulation mechanism, energy partitioning is shown to vary with prevailing environmental conditions. In this investigation, energy absorbed during periods of moderate photosynthetically active radiation (PAR < 1200 moLm(-2)s(-1)) was largely allocated towards photochemistry (phi(PSII)) with nominal amounts to thermal dissipation through reversible thermal dissipation (phi(NPQr)). In extremely high solar radiation (PAR > 1500 moLm(-2)s(-1)) or in a cold temperature (T-a < 0 degrees C), more energy was dissipated by way of non-regulated thermal energy (phi(f,D)) and sustained thermal dissipation (phi(NPQs)), leading to non-reversible photoinhibition or photodamage. This was mainly as a result of the low utilization and high absorption of light energy by PSII under cold conditions and physiologically-induced vulnerability. It was concluded that Salix psammophila had a clear tolerance to high temperatures and moderate solar radiation, but tended to be more vulnerable to high solar radiation and cold temperature. Based on species sensitivity to extreme environmental conditions, practical application and extension of Salix psammophila for land-restoration purposes should be approached cautiously, especially in high-latitude or high-altitude desert ecosystems commonly affected by events of high solar radiation and cold temperature.