氮磷硅添加对青藏高原高寒草甸垂穗披碱草叶片碳氮磷的影响

以甘南高寒草甸常见牧草垂穗披碱草(Elymus nutans)为研究对象,比较不同氮磷硅添加下,垂穗披碱草叶片对元素添加的反应。研究发现:氮添加显著提高土壤中硝态氮和铵态氮的含量;磷添加提高了土壤中全磷和速效磷的含量;高浓度的硅单独、硅与氮或磷混合可提高土壤中硝态氮的含量或全磷和速效磷的含量;氮和磷单独添加分别能提高垂穗披碱草叶片全氮和全磷含量,高浓度的硅单独、硅与氮或磷混合添加都能提高垂穗披碱草叶片全氮和全磷的含量。就硅元素而言,高浓度的硅添加,硅与氮或磷混合添加能提高土壤硝态氮、全磷和速效磷的含量,促进垂穗披碱草对土壤中氮磷的吸收,从而使植物叶片中氮磷的含量增加。

Effects of nitrogen, phosphorus and silicon addition on leaf carbon, nitrogen, and phosphorus concentration of Elymus nutans of alpine meadow on Qinghai-Tibetan Plateau, China

Elymus nutans, widely distributed in natural and cultivated pastures with favorable forage yield, good quality and adaptability to local environment, plays an important role in animal husbandry and environmental sustainability on Qinghai-Tibetan Plateau, China. Silicon (Si) is not considered as an essential element for higher plants and thus is believed to have no effect on primary metabolism in unstressed plants. But previous studies have shown that silicon can promote nutrient root absorption and enhance plant productivity in various plant species such as rice, alfalfa and celery. In greenhouse study, silicon nutrition improves root absorption of nitrogen and phosphorus; however, no attempt has been made to study the absorption of nitrogen and phosphorus in root and the content of nitrogen and phosphorus in leaf when silicon, nitrogen and phosphorus were added at different concentration in field. A study was conducted with Elymus nutans to address the physiological effect caused by the addition of these elements. Sixteen treatments consisted of: three rates of nitrogen addition: 7, 14, 21 g/m²; three rates of phosphorus addition: 4.92, 9.84, 14.76 g/m²; three rates of available silicon addition: 0.718, 1.436, 2.154 g/m²; three rates of nitrogen and one rate of silicon addition: nitrogen 7, 14, 21 g/m² and silicon 1.436 g/m²; three rates of phosphorus and one rate of silicon addition: phosphorus 4.92, 9.84, 14.76 g/m² and silicon 1.436 g/m²; and one control: neither nitrogen and phosphorus nor silicon addition. Each treatment was replicated six times. Results showed that in soil, nitrogen addition alone enhanced contents of NH₄⁺-N (P<0.001) and NO₃^--N (P<0.001). Silicon addition alone or addition with phosphorus did not affect NH₄⁺-N content. Phosphorus addition alone enhanced total and available phosphorus contents. Low concentration silicon addition alone did not affected NO₃^--N (P>0.5) content, or total and available phosphorus content (P>0.5). High concentration silicon addition alone, silicon addition with nitrogen or phosphorus together increased NO₃^--N content (P<0.001), or total and available phosphorus content (P<0.001). In leaf of E. nutans, nitrogen and phosphorus addition alone enhanced total nitrogen and phosphorus content. Low concentration silicon addition alone did not affect total nitrogen and phosphorus content. High and moderate concentration silicon addition alone, silicon addition with nitrogen or phosphorus together can increase leaf of total nitrogen and phosphorus content. There were significant linear positive relationships between total nitrogen content in leaf of E. nutans and soil NH₄⁺-N (R²=0.96, P<0.001) and NO₃^--N content (R²=0.91, P<0.001) and also between leaf total phosphorus and soil total phosphorus (R²=0.88, P<0.001) and soil available phosphorus content (R²=0.96, P<0.001). In the field experiment, silicon can promote the uptake of nitrogen and phosphorus by E. nutans. These results suggested that silicon application is useful to increase leaf nitrogen and phosphorus content of E. nutans through the enhancement of NO₃^--N, total and available phosphorus content in soil. We identify Si nutrition as an important target in attempts to improve the uptake of nitrogen and phosphorus by E. nutans.