The present study aims to investigate the differences in leaf pigment content and the photosynthetic characteristics under natural and low light intensities between the Chinese nativePhysocarpus amurensis Maximand the importedPhysocarpus opulifolius“Diabolo” from North America. We aim to discuss the responses and the adaptive mechanism of these two cultivars ofPhysocarpusto a low light environment. The results show that the specific leaf area (SLA) and the chlorophyll content were significantly increased in the leaves of bothPhysocarpuscultivars in response to a low light intensity, and the SLA and chlorophyll content were higher in the leaves of low light-treatedP. opulifolius“Diabolo” compared with the leaves of low light-treatedP. amurensis Maxim. Moreover, the content of anthocyanin was markedly reduced in the leaves ofP. opulifolius“Diabolo” under low light intensity, which allowed for a greater capacity of photon capture under the low light condition. Under natural light, the photosynthetic carbon assimilation capacity was greater in the leaves ofP. amurensis Maximcompared with the leaves ofP. opulifolius“Diabolo” that were rich with anthocyanin. However, in response to low light, AQY,P_max, LCP and LSP decreased to a lesser extent in the leaves ofP. opulifolius“Diabolo” compared with the leaves ofP. amurensis Maxim. These results suggest thatP. opulifolius“Diabolo” exhibits a greater ability in adaption to low light, and it is probably related to the relatively higher chlorophyll content and the smaller SLA in the leaves ofP. opulifolius“Diabolo.” In addition, the low light intensity resulted in a reduced photochemical activity of photosystem (PS) II in the leaves of bothPhysocarpus, as evidenced by increased values of the relative variable fluorescence at point J and point I on the OJIP curve. This result suggests that the electron acceptor in PS II was the major responsive site to the low light stress in the leaves of bothPhysocarpuscultivars, and that the low light intensity significantly inhibited electron transfer on the acceptor side of PS II and reduced the activity of the oxygen-evolving complex (OEC) in the leaves of bothPhysocarpuscultivars. The PS II function inP. opulifolius“Diabolo” was higher than that inP. amurensis Maximin response to low light. Under low light, the composition of photosynthetic pigments was altered in the leaves ofP. opulifolius“Diabolo” in order to maintain a relatively high activity of primary photochemical reactions, and this is the basis of the greater photosynthetic carbon assimilation capacity and one of the main reasons for the better shade-tolerance inP. opulifolius“Diabolo.”

In this study, the effects of inoculating arbuscular mycorrhizal fungi (Glomus mosseae) on the growth, chlorophyll content, photosynthetic gas exchange parameters, and chlorophyll fluorescence characteristics of Lolium perenne L. in cadmium (Cd) contaminated soil were investigated. The results showed that the root vigor of L. perenne declined, while the chlorophyll content significantly decreased with the increase of Cd content, especially the chlorophyll a content in leaves. The photosynthetic carbon assimilation capacity and PSII activity of L. perenne leaves were also significantly inhibited by Cd stress, especially the electron transfer at the receptor side of PSII, which was more sensitive to Cd stress. The infection level of G. mosseae on L. perenne roots was relatively high and inoculation with G. mosseae increased the mycorrhizal infection rate of L. perenne roots up to 50–70%. Due to the impact of the mycorrhizal infection, the Cd content in L. perenne roots was significantly increased compared to non-inoculated treatment; however, the Cd content in the aboveground part of L. perenne was not significantly different compared to the non-inoculated treatment. After inoculation with G. mosseae, the root vigor of L. perenne increased to some extent, alleviating the chlorophyll degradation in L. perenne leaves under Cd contaminated soil. Infection with G. mosseae can improve the stoma limitation of L. perenne leaves in Cd contaminated soil and increase the non-stomatal factors including the tolerance of its photosynthetic apparatus to Cd, to improve photosynthetic capacity. G. mosseae infection can improve the photosynthetic electron transport capacity of PSII in L. perenne leaves under Cd stress and promotes the activity of the oxygen-evolving complex to different degrees at the donor side of PSII and the electron transport capacity from Q_A to Q_B on the receptor side of PSII. Thus, this guarantees that L. perenne leaves inoculated with G. mosseae in Cd contaminated soil have relatively higher PSII activity. Therefore, inoculation with G. mosseae can improve the capacity of Cd tolerance of L. perenne with regard to various aspects, such as morphological characteristics and photosynthetic functions, and reduce the toxicity of Cd on L. perenne.

This study investigated the effect of NaCl stress on Na⁺ and K⁺ absorption and transport by roots, nitrogen and phosphorus content in leaves, PSII photochemical activity and reactive oxygen species (ROS) in leaves of mulberry own-root seedlings and grafted seedlings. To determine the response, own-root seedlings of a high yielding mulberry cultivar, Tieba mulberry (Morus alba L.), and the grafted seedlings, obtained by using Qinglong mulberry with high salt tolerance as rootstock and Tieba mulberry as scion, were used. The Na⁺ content in roots and leaves of grafted seedlings was significantly lower than that in own-root seedlings under salt stress; while K⁺ content in roots and leaves of grafted seedlings was significantly higher than that in own-root seedlings. The root activity in grafted seedlings was significantly higher than that in own-root seedlings, as well as the content of nitrogen, phosphorous and water. PSII photochemical activity in leaves of grafted seedlings was less significantly affected by salt stress compared to own-root seedlings. The electron transport at the acceptor side of PSII from Q_A to Q_B was less affected by salt stress, which resulted in a significantly lower ROS content in leaves of grafted seedlings than that of own-root seedlings. Therefore, grafting high-yielding and good-quality Tieba mulberry with salt tolerant Qinglong mulberry as rootstock showed a relatively high salt tolerance. This may be because (1) the root system of rootstock presented high Na⁺ resistance and has selective absorption capacity for Na⁺ and K⁺ (2) the root system of rootstock prevented excess Na⁺ from being transported to aerial parts in order to reduce adverse effects of Na⁺ (3) the root system of rootstock had enhanced root activity under salt stress, which accelerated water and nutrient absorption (4) the leaves of grafted seedlings had higher PSII photochemical activity and electron transport rate compared with those of own-root seedlings under salt stress, which effectively reduced ROS burst mediated by photosynthesis and reduced oxidative damage.

The effects of arbuscular mycorrhizal fungi Glomus mosseae (+AMF) on the growth, nutrient uptake and leaf photosynthetic characteristics of alfalfa (Medicago sativa) under salt stress were studied. In alfalfa, 100 mM salt stress had no obvious effect on plant growth, nutrient content and photosynthetic capacity, however, 200 mM salt stress significantly inhibited biomass accumulation and NPK uptake. In addition, 200 mM salt stress led to decreased photosynthetic carbon assimilation capacity and lower PSII and PSI activity levels. Cultivation of alfafa with +AMF promoted biomass accumulation and uptake of nutrients, increased its underground growth, and promoted accumulation of P over N and K. +AMF increased PSII and PSI activities in alfalfa leaves under salt stress, and increased the electron transfer ability of PSII donor and acceptor sides. +AMF not only made alfalfa have relatively high stomatal conductance under salt stress, but also significantly enhanced its ability to utilize CO₂.