Water and nitrogen stresses are major constraints for agricultural and forest productivity. Although the effects of water scarcity or nitrogen stress on plant growth, physiology, and yield have been widely studied, few studies have assessed the combined effects of both stresses. In the present study, we investigated the effects of different nitrogen forms (NO3−N, NH4+-N, and a combination of NO3−N + NH4+-N) on antioxidant enzyme activity, osmotic regulatory substances, and nitrogen assimilation in Chinese fir (Cunninghamia lanceolata) plantlets under drought stress (induced by 10% polyethylene glycol). We found that different N ionic forms had different effects on drought-stressed plantlets. Nitrogen supply greatly increased the activities of superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO) when plantlets were exposed to water stress. The malondialdehyde (MDA) contents significantly decreased under the NH4+ + water stress treatment. The proline (Pr) contents significantly increased in both the NO3−N and NH4+-N + water stress treatment. The nitrate reductase (NR) increased by 7.1% in the NO3− + water stress treatment, and the glutamine synthetase (GS), and the glutamate synthase (GOGAT) activity increased in all the nitrogen + water stress treatments. These results suggested that nitrogen supply could alleviate the adverse effects of drought stress on plants by enhancing antioxidant defense and improving nitrogen assimilation, while the effects on plant tolerance to drought stress varied with nitrogen ionic forms.

This study examines the effects of light emitting diodes (LEDs) on tissue culture proliferation of Acacia melanoxylon plantlets among five different clones (FM1, FM2, FM4, FM5, and FM10). Shoot bud apex cuttings were transplanted onto Murashige and Skoog basal medium containing 0.1 mg L-1 6-benzyladenine and 0.5 mg L-1 naphthalene acetic acid and cultured in vitro for 40 days. Root growth was studied under different light intensities and photoperiods ex vitro. The bud proliferation coefficient was greatest under a light intensity of 45 μmol m-2 s-1 photosynthetic photon flux and photoperiod of 16 h light, but decreased as the light intensity increased. However, the greatest light intensity was beneficial for the growth of robust plantlets. Plantlets exposed to red and blue LED combinations grew tall and green, with a small number of roots. Plantlets also grew taller and some roots expanded under the longer photoperiod. Increased light intensity had positive effects on root number and rooting rate, and prolonged light greatly increased root number. Therefore, lower light intensity and a short photoperiod were beneficial for bud proliferation, while red/blue LED combinations, increased light intensity, and longer light illumination were beneficial for plantlet growth and root growth of Acacia melanoxylon.

As part of the plant water-use process, plant nocturnal sap flow (Qn) has been demonstrated to have important ecophysiological significance to compensate for water loss. The purpose of this study was to explore nocturnal water-use strategies to fill the knowledge gap in mangroves, by measuring three species co-occurring in a subtropical estuary. Sap flow was monitored over an entire year using thermal diffusive probes. Stem diameter and leaf-level gas exchange were measured in summer. The data were used to explore the different nocturnal water balance maintaining mechanisms among species. The Qn existed persistently and contributed markedly over 5.5%~24.0% of the daily sap flow (Q) across species, which was associated with two processes, nocturnal transpiration (En) and nocturnal stem water refilling (Rn). We found that the stem recharge of the Kandelia obovata and Aegiceras corniculatum occurred mainly after sunset and that the high salinity environment drove higher Qn while stem recharge of the Avicennia marina mainly occurred in the daytime and the high salinity environment inhibited the Qn. The diversity of stem recharge patterns and response to sap flow to high salinity conditions were the main reasons for the differences in Qn/Q among species. For Kandelia obovata and Aegiceras corniculatum, Rn was the main contributor to Qn, which was driven by the demands of stem water refilling after diurnal water depletion and high salt environment. Both of the species have a strict control over the stomata to reduce water loss at night. In contrast, Avicennia marina maintained a low Qn, driven by vapor pressure deficit, and the Qn mainly used for En, which adapts to high salinity conditions by limiting water dissipation at night. We conclude that the diverse ways Qn properties act as water-compensating strategies among the co-occurring mangrove species might help the trees to overcoming water scarcity.

As part of the plant water-use process, plant nocturnal sap flow ( Q) has been demonstrated to have important ecophysiological significance to compensate for water loss. The purpose of this study was to explore nocturnal water-use strategies to fill the knowledge gap in mangroves, by measuring three species co-occurring in a subtropical estuary. The Q existed persistently and contributed markedly over 5.5%~24.0% of the daily sap flow ( Q) across species, which was associated with two processes, nocturnal transpiration ( E) and nocturnal stem water refilling ( R). The diversity of stem recharge patterns and response to sap flow to high salinity conditions were the main reasons for the differences in Q/ Q among species. For Kandelia obovata and Aegiceras corniculatum, R was the main contributor to Q, which driven by the demands of stem water refilling after diurnal water depletion and high salinity. In contrast, Avicennia marina maintained a low Q, driven by vapor pressure deficit, and the Q mainly used for E, which adapts to high salinity conditions by limiting water dissipation at night. We conclude that the diverse ways Q properties act as water-compensating strategies among the co-occurring mangrove species might help the trees to overcoming water scarcity.