Effects of Grazing Intensity on Plant-Soil C: N: P Stoichiometry with Precipitation Changes During the Growing Season in Desert Grassland

Background and aimsHigh-intensity grazing in the Mongolian grassland has led to the general deterioration of biodiversity and ecosystem functioning. Although abundant evidence shows that grazing affects the structure and function of grassland ecosystems, research on the impact of precipitation, especially under drought and overgrazing. MethodsWe examined the effects of heavy grazing, moderate grazing and no grazing on plant communities; plant and soil C, N and P contents; and plant and soil C:N:P stoichiometry in the desert grassland in different years with different amounts of precipitation. ResultsThere was no significant difference in the species diversity between the grazing and no grazing treatment, while the no grazing treatment was significantly higher than the heavy grazing treatment. Compared with the amounts in the no grazing and moderate grazing treatments, the N and P contents of the plants in the heavy grazing treatment were the highest, and the N content of the soil increased. There was a positive correlation between precipitation and the N and P contents of plants and the C and N contents of the soil at 0-10 cm and 10-20 cm. ConclusionsOur study suggest that a large amount of precipitation of plant growth will drive changes in the community species diversity. Grazing promoted the flow of N between plants and the soil, especially under heavy grazing. Under grazing stress, plants maintain the potential of compensatory growth, and precipitation in the peak season of plant growth induces rapid growth, suggesting that precipitation is an important factor driving grazing ecosystems.

Water deficit modifies C:N:P stoichiometry affecting sugarcane and energy cane yield and its relationships with silicon supply

Climate change has increased the occurrence of water deficit in regions where sugarcane and energy cane are cultivated, jeopardizing dry matter production of stems. It was hypothesized that the reasons behind this fact relate to C:N:P stoichiometric modifications in these species that impair the conversion rates of accumulated nutrients in the stems, which could be attenuated by supplying silicon (Si) to the crops. Thus, the aims of this study were to evaluate the effects of water deficit in sugarcane and energy cane ratoons in the presence and absence of Si, in the C:N:P stoichiometry of stems, in the use efficiency of these nutrients and in the accumulation of dry matter in stems. Two experiments were carried out, using sugarcane (Saccharum officinarum) and energy cane (S. spontaneum), cultivated in pots filled with a Typic Quartzipisamment. The treatments for both experiments were arranged in a factorial scheme 2 × 2, without (70% of the soil’s water retention capacity) and with (30% of the capacity) water deficit, without and with the application of Si via fertirrigation, associated with foliar pulverization, both at a concentration of 2.5 mmol L−1, arranged in randomized blocks. The reduction in dry matter production of stems in both species caused by water deficit was due to modifications of the C, N and P stoichiometric homeostasis, but the benefit of Si in these plants when increasing dry matter production was not a reflection of the change in homeostasis, thus it may be involved in other mechanisms that remain unknown and should be further studied.

Silicon Changes C:N:P Stoichiometry and Favors Pre-Sprouted Seedling Growth, Yield and the Technological Quality of Sugarcane.

The importance of silicon (Si) in sugarcane is well known, but its effects on changing C:N:P stoichiometry enough to increase pre-sprouted seedling (PSS) and sugarcane development in the field remains unknown. To that end, the present study aimed to assess whether Si fertigation favors its absorption enough to change elemental stoichiometry (C:N:P), physiological attributes and PSS growth, as well as the growth, stem yield and juice quality of sugarcane. Two field experiments were conducted in the PSS formation stage and another in the sugarcane plant development phase. Experiment 1 was carried out in a greenhouse with PSSs under two treatments: in the absence and presence of Si (2 mmol L−1) fertigation. Experiment 2 was performed in the field in red-yellow argisol with the sugarcane plant undergoing the following treatments: absence of Si (No Si); Si supplied by fertigation during the PSS formation and sugarcane plant development phases (Si–C); and Si supplied during the PSS formation and sugarcane plant development phases (Si–M+C). The following were assessed in experiment I: growth, leaf green color index (GCI), chlorophyll fluorescence, C, N, P, and Si content, and C:Si, C:N and C:P stoichiometric ratios. In experiment II, the same stoichiometric ratios were assessed, as well as sugarcane growth, stem yield and juice quality. Si reduced the C:Si, C:N and C:P stoichiometric ratios in PSS. The C:Si ratio in the leaves and stems declined with the supply of Si, while the C:N and C:P ratio in the leaves and stem was higher in plants that received Si in the Si-M+C treatment. Applying Si fertigation in PSS formation to promote changes in C:N:P stoichiometry favored photosynthetic efficiency and growth. The Si–M+C treatment stood out, since it also caused enough C:N:P stoichiometric changes to increase sugarcane growth, yield and juice quality.