J Plant Ecol ›› 2020, Vol. 13 ›› Issue (5): 633-640.DOI: 10.1093/jpe/rtaa050

• Research Articles • Previous Articles     Next Articles

Nitrogen and phosphorus translocation of forest floor mosses as affected by a pulse of these nutrients

Xin Liu1,2, * , Zhe Wang2,3 , Xiaoming Li2 and Weikai Bao2, *   

  1. 1 Ecological Security and Protection Key Laboratory of Sichuan Province, Mianyang Normal University, Mianyang 621000, China, 2 Chinese Academy of Sciences (CAS) Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China, 3 College of Life Sciences, Shanghai Normal University, Shanghai 200234, China

    *
    Corresponding author. E-mail: liuxin1@cib.ac.cn (X.L.); baowk@cib.ac.cn (W.B.)
  • Received:2019-06-12 Revised:2019-06-10 Accepted:2020-08-04 Online:2020-08-11 Published:2020-10-01

Abstract:

Aims

Mosses are dominant in many ecosystems where nutrients from deposition are one of the main nutrient sources. However, it is difficult to evaluate mosses’ role in nutrient cycling without knowledge of how mosses use deposited nutrient inputs. To fill this gap, the present study aims to investigate: (i) how nitrogen (N) and phosphorus (P) concentrations of new-grown segments change along a gradient of N or P amount in a pulse treatment? (ii) how do a pulse of major nutrient (N or P) affect N or P translocation rate along a moss shoot? and (iii) to what extent do N or P translocation rates link to nutrient status of the new-grown segments of mosses?

Methods

We measured N and P concentrations of segments with different ages in two dominant forest floor mosses, Actinothuidium hookeri and Hylocomium splendens, on 8 days and 1 year after N and P pulse treatment with an in situ experiment in a subalpine fir forest in eastern Tibetan Plateau.

Important Findings

Both mosses were efficient in taking up nutrients from a pulse of either N or P. Nitrogen and P concentrations of new-grown segments were affected by nutrient pulse treatments. These N and P concentration changes were attributed to the initial N and P concentration of the young segments harvested 8 days after nutrient pulse treatments, suggesting that the captured nutrients were reallocated to the new-grown segments via translocation, which was largely controlled by a source–sink relationship. While no significant relationship was found between N translocation rate and N:P ratio of the new-grown segments, P translocation rate explained 21%–23% of the variance of N:P ratio of the new-grown segments, implying importance of P transport in supporting the new-grown sections. These results suggest that nutrient (N, P) translocation is a key process for mosses to utilize intermittent nutrient supply, and thus make mosses an important nutrient pool of the ecosystem.

Key words: forest floor mosses, nutrient resorption, nutrient cycling, nutrient pulse, old-growth forest

摘要:
藓类是亚高山森林、北方针叶林和极地苔原等原始生态系统的重要组成部分。养分沉降是这些生态系统的主要养分来源。然而,对 藓类如何利用大气沉降这一时间上异质性较高的养分来源的认识缺乏,限制了我们对藓类在生态系统养分循环中作用的认识,也制约了模 拟和预测生态系统服务功能动态变化的有效性。本研究中,我们重点关注如下问题:(1)藓类新生部分的氮、磷含量随氮或磷沉降量的变化; (2)氮或磷养分沉降如何影响藓类的氮磷转运;(3)氮磷转运与藓类新生部分养分含量的关联性?为此,我们在位于青藏高原东部的亚高山 冷杉林中开展了设置有不同氮、磷施加量水平的突发养分沉降实验。以林下优势度最高的塔藓和锦丝藓为对象,我们在施加实验处理8天和1年后,分别测定了不同年龄藓类茎段中的氮、磷含量。研究结果发现,养分处理8天后,锦丝藓和塔藓的所有茎段的氮或磷含量均随处理中氮或磷施加量的增加而增加,表明它们能够高效率地吸收施加的氮或磷。养分处理1年后,形成于养分处理后的新生茎段中的氮、磷含量以及氮磷比与处理后8天的藓类茎段中氮、磷含量以及氮磷比呈正相关关系,表明藓类将吸收的养分转运至新生部分,转运过程受源—库关系的调控。磷转运效率解释了新生茎段21%–23%的氮磷比变化,而氮转运与新生茎段氮磷比没有显著关系,结果暗示磷转运对藓类生长的重要性。上述结果表明,养分转运是藓类植物利用间断的沉降养分的关键机制,也使藓类成为生态系统中重要的养分库。

关键词: 林下藓类, 养分回收, 养分循环, 突发养分沉降, 老龄林