林地覆盖经营对雷竹鞭根主要养分内循环的影响

为了给林地覆盖经营雷竹(Phyllostachys violascens)林可持续经营提供理论参考,探讨了休养式覆盖经营(覆盖3a后休养3a)、长期覆盖经营(覆盖6a)和不覆盖雷竹林(CK)2年生壮龄竹鞭及其1级、2级根N、P、K、Mg、Ca、Fe浓度和养分迁移、内循环率的差异。结果表明:不同覆盖经营年限雷竹林N、P、K、Mg、Ca和Fe浓度总体上1级根显著高于2级根。1级根和2级根中均存在N、P、K、Mg的养分内循环,且1级根养分内循环率大于2级根,Fe、Ca内循环不明显。N、P、K、Mg养分浓度与养分迁移速率随时间的推延,1级根为持续降低,2级根为先升高后降低。与不覆盖雷竹林相比,休养式林地覆盖经营总体上提高了1级、2级根的N、P、K、Ca的浓度和P、K、Mg的迁移速率、N、P、K的迁移量、P、K的养分内循环率以及1级根Mg的浓度和迁移量、2级根N的迁移速率和Mg的内循环率;长期林地覆盖经营虽提高了雷竹1级根N、K的浓度和N的迁移量及2级根N的浓度和内循环率,但总体上降低了1级根P、K、Mg和2级根N、P、Mg的迁移量与1级、2级根P、Mg的迁移速率及P、K、Mg的养分内循环率。研究表明:雷竹林鞭根中存在明显的养分内循环,且1级根对养分内循环的贡献较大。休养式林地覆盖经营利于雷竹林对养分的循环利用,而长期覆盖经营阻碍了根系对养分的平衡吸收,减弱了根系养分的内循环,不利于雷竹林的生长更新。

Effects of mulching management on the internal cycling of nutrients in the rhizomatous roots of Phyllostachys violascens

Although fine roots constitute only a small part of the biomass of root systems, they significantly facilitate the uptake of nutrients from soils, and therefore play a very important role in the flow of energy and matter in the biosphere. The nutrient cycle in fine roots is accordingly of particular importance in enhancing the nutrition efficiency of plants. However, the internal cycling of nutrients in fine roots during senescence has, for a long time, been an issue of some controversy. Moreover, fine roots are very sensitive to environmental stress factors, such as those due to soil nutrient and water deficiency, temperature, and CO₂ concentration, which affect the characteristics and, in turn, the nutrient absorption and utilization of fine roots. However, despite its important role in plant nutrition, the senescence mechanism of fine roots is still unclear. As a bamboo species with high yield and efficiency, based on excellent regeneration of its shoots, Phyllostachys violascens is typically affected by frequent and severe artificial disturbance. Although mulching management is commonly employed in P. violascens plantations, in some plantations the practice of mulching and fertilization under intensive cultivation management has seriously affected the health of P. violascens stands. The present study was conducted in order to elucidate the mechanism underlying the deleterious effects of mulching on P. violascens stands and to provide theoretical guidance for the regeneration of degraded bamboo stands. We determined the N, P, K, Mg, Ca, and Fe concentrations in the rhizome and the first and second rhizome roots of P. violascens plants subjected to three different treatments: respite mulching (mulched for 3 years and rested for 3 years), long-term mulching (6 years continuous mulching), and no mulching (CK). The results showed that, in all stands, N, P, K, Mg, Ca, and Fe concentrations in the first roots were significantly higher than those in the second roots. Furthermore, there was an obvious internal cycling of N, P, K, and Mg in the first and second roots, and the internal cycling rate of these nutrients in the first roots was significantly higher than that in the second roots. For Fe and Ca, however, there was no significant internal cycling. With an increase in the length of the trial, there was a decrease in the concentrations of N, P, K, and Mg and a decrease in the retranslocation rates of these nutrients in the first roots. In the second roots, there were initial increases in the concentrations and retranslocation of these nutrients, but these subsequently declined. Compared with CK, respite mulching led to significant increases in N, P, K, and Ca concentrations, P, K, and Mg retranslocation rates, N, P, and K migration, and P and K internal cycling rates in the first and second roots. Respite mulching also resulted in significant increases in the concentration and migration of Mg in the first roots, and in the retranslocation rate of N and the internal cycling rate of Mg in the second roots. Furthermore, long-term mulching led to a significant increase in N and K concentrations and N migration in the first roots, and in the N concentration and internal cycling rate in the second roots. In contrast, long-term mulching resulted in significant decline in P, K, and Mg migration in the first roots and in N, P, and Mg migration in the second roots, and in P and Mg retranslocation rates and P, K, and Mg internal cycling rates in the first and second roots. Thus, it can be concluded that there was an obvious internal cycling of N, P, K, and Mg in the first and second rhizome roots of P. violascens, and that the first roots made a larger contribution to nutrient cycling. Moreover, whereas respite mulching proved to be beneficial for internal nutrient cycling, long-term mulching hindered the absorption of nutrients, and reduced internal cycling, which was detrimental to the growth and regeneration of P. violascens.