Scholarly article on topic 'Competitive Hierarchy among Three Perennial Grasses under Clipping and Fertilization through Three Growing Years on the Eastern Qinghai-Tibetan Plateau'

Competitive Hierarchy among Three Perennial Grasses under Clipping and Fertilization through Three Growing Years on the Eastern Qinghai-Tibetan Plateau Academic research paper on "Agriculture, forestry, and fisheries"

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Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — M.H. Gu, T. Wang, Z.K. Xie

Abstract The meadow ecosystem of the Qinghai-Tibetan plateau, the largest rangeland in China, has been degenerating recently from heavy grazing and soil erosion, resulting in decreased carrying capacity and canopy coverage. A field experiment studied the competitive hierarchy among three perennial grasses, Elymus nutans, Festuca sinensis, and Festuca ovina, which distributed widely on the east Qinghai-Tibetan plateau. There were three two-species mixtures at four seeding densities at two fertilization levels and three clipping residual heights measured over three years. Shoot biomass and Relative Competitive Intensity were determined from harvested shoot dry weights. The results showed that E. nutans was a competitive winner in all of the mixtures, regardless of treatments. F. sinensis and F. ovina were inferior competitors compared with E. nutans. The shoot biomass and Relative Competitive Intensity were greatest for E. nutans, then F. sinensis, and least for F. ovina in the 2nd year but in the 3rd year F. ovina surpassed F. sinensis. Fertilization and clipping treatments had significant effect on species’ shoot biomass and no significant effects on Relative Competitive Intensity. The results showed that the mixtures of E. nutans / F. sinensis and E. nutans / F. ovina are appropriate mixture combinations to maintain high shoot biomass and stable community patterns on the Qinghai-Tibetan plateau. They are good choice to improve grassland, and provide benefits for both local economic development and environmental protection.

Academic research paper on topic "Competitive Hierarchy among Three Perennial Grasses under Clipping and Fertilization through Three Growing Years on the Eastern Qinghai-Tibetan Plateau"

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Environmental Sciences

Procedia Environmental Sciences 13 (2012) 151 - 157 ^^^^^^^^^^^^^^^^^^^

The 18th Biennial Conference of International Society for Ecological Modelling

Competitive Hierarchy among Three Perennial Grasses under Clipping and Fertilization through Three Growing Years on the Eastern Qinghai-Tibetan Plateau

M. H. Gu, T. Wang*, Z. K. Xie

Cold and Arid Regions Environmental and Engineering Research Institute, CAS Lanzhou, 730000, China.a

Abstract

The meadow ecosystem of the Qinghai-Tibetan plateau, the largest rangeland in China, has been degenerating recently from heavy grazing and soil erosion, resulting in decreased carrying capacity and canopy coverage. A field experiment studied the competitive hierarchy among three perennial grasses, Elymus nutans, Festuca sinensis, and Festuca ovina, which distributed widely on the east Qinghai-Tibetan plateau. There were three two-species mixtures at four seeding densities at two fertilization levels and three clipping residual heights measured over three years. Shoot biomass and Relative Competitive Intensity were determined from harvested shoot dry weights. The results showed that E. nutans was a competitive winner in all of the mixtures, regardless of treatments. F. sinensis and F. ovina were inferior competitors compared with E. nutans. The shoot biomass and Relative Competitive Intensity were greatest for E. nutans, then F. sinensis, and least for F. ovina in the 2nd year but in the 3rd year F. ovina surpassed F. sinensis. Fertilization and clipping treatments had significant effect on species' shoot biomass and no significant effects on Relative Competitive Intensity. The results showed that the mixtures of E. nutans / F. sinensis and E. nutans / F. ovina are appropriate mixture combinations to maintain high shoot biomass and stable community patterns on the Qinghai-Tibetan plateau. They are good choice to improve grassland, and provide benefits for both local economic development and environmental protection.

© 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of School of Environment, Beijing Normal University.

Keywords: competitive hierarchy; clipping; fertilization; Qinghai-Tibetan

* Corresponding author. Tel.: +86-0931-8277753.

E-mail address: wangtao@lzb.ac.cn.

1878-0296 © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of School of Environment, Beijing Normal University. doi:10.1016/j.proenv.2012.01.015

1. Introduction

Ecologists generally agree that competition often has a major role in structuring communities, especially in plants [1-3]. However, estimates of competitive ability in plants are most often based on the relative intensity of size suppression experienced by competitors at a single life stage in experimental studies [4-5]. Far fewer studies record relative success in terms of survival and fecundity under competition [6-8]. 70% of the studies were conducted over only a single growing season. Only 1% of the surveyed studies have accounted for the possible effects of variables including growth and survival [6-7]. Studies have already shown that measurement of only one of the traits can lead to erroneous conclusions/predications. It is essential, therefore, that long-term study including all of these component traits be measured or at least interpreted as part of the underlying assumptions when evaluating the relative competitive abilities of plants.

The experiment was designed using three perennial grass species, dlymus nutans, Festuca sinensis, and Festuca /vina, which are widely distributed in the alpine meadow of Qinghai-Tibetan Plateau. The three grasses are important and excellent grass in grasslands of cooler regions because of high quality and winter hardiness. d. nutans is a tall (800-1300 mm), broad-leaved (4-8 mm) and tufted species, which has many large leaves spreading along its stem. F. sinensis is moderately tall (400-700 mm), narrow-leaved (2-4 mm) species with leaf growth similar to d. nutans. F /vina is a short (100-350 mm) and strongly tufted species with many narrow (0.5-1.5 mm) needle-like leaves from a low base. In this experiment, the competition ability among the three species was investigated over three years under different fertilizer and clipping treatments. This involves both the competition between species and their combined yield. Reader [9] first used the index Relative Competition Intensity (RCI) by equation (1). Several researches have concluded that RCI is an appropriate index with higher RCI values is suggesting that species is an inferior competitor[10]. The aim was to find the optimum mixture combinations and reasonable agriculture treatments to identify a sustainable development and management pattern for stockbreeding and protecting vegetation of the perennial rangeland on the Qinghai-Tibetan Plateau.

2. Methods

2.1. Study site and materials

The experiment was performed at the Ecosystem Orientation Research Station of Lanzhou University in an alpine meadow located on the east of Tibetan Alpine meadow of China (N34°55', Wl02°53'). The site has an altitude of 2900 m.a.s.l., 557 mm annual average rainfall (occurring mainly in summer) and annual temperature of 2°C. The site was fenced in April 2000 and was subsequently only grazed during the winter so the shoot biomass was not changed in the period of experiment. Seeds were collected in September 2002 for sowing in the experiment June 2003. The trial was sown into a previously herbicide sprayed and disk-cultivated field site on 21-Jun 2003.

2.2. Experiment design

It was main plots were 24 randomized combinations of 6 species combinations for the 3 species (3 pair-wise and 3 monoculture) and 4 seeding densities with 4 spatial replications. Within those were 6 combinations of 2 fertilization levels and 3 clipping levels. The four seeding densities were 400, 800, 1600 and 3200 seed m-2 and the proportions of seeds was 50:50 for each species in the pairwise mixtures, the two annual fertilization levels nil or 900 kg ha 1 of (NH4)2HPO4 and the three clipping levels were unclip, clip to a 60 mm residual height and clip to a 20 mm residual height. The main plots were 3 X 4m

with 0.5 m guard strip between plots, and each split-plot was 1.5 X 1.3 m with samplings from a central 0.25 x 0.25 m marked quadrat. The fertilization treatment was applied after re-growth commenced in April of the 2nd and 3rd year. The half of the plots swards were fertilized with granular urea-N (granules around 2 mm diameter) by hand after rainfall. Clipping treatments were harvested twice (12 June, 20 July), and all plots were harvested on 5-Sept in the 2nd year. For the 3rd year the corresponding dates were 10 June, 20 July and 8-Sept. The shoot biomasses in the results were the total dry weights of the June, July and September samplings.

2.3. Data analyses

In this experiment, the RCI competition index of species was based on shoot biomass. Analysis used General Linear ANOVA statistics (Type III sum of squares) for split-plot design by SPSS13.0.

3. Results

3.1. Sh//t bi/mass

The ANOVA of fertilization and clipping in split-plots on the shoot biomass for the three species were as follows. Fertilization and clipping all had highly significant (P<0.001) effects on each of the species' shoot biomass. The interaction between the two treatments had no significant effect on each of the species' shoot biomass. Multiple comparisons among clipping levels showed, unclipping and two clipping residuals had highly significant difference respectively (P<0.001), and two clipping residuals had no significant difference (P>0.05) for d. nutans and F. sinensis shoot biomass, and the difference among three clipping levels were all highly significant (P<0.01) for F. /vina shoot biomass. The ANOVA of year in main plots on the shoot biomass for the three species showed that year had highly significant effect (P<0.001) on each of the species' shoot biomass. In d. nutans / F. sinensis mixture, fertilization increased species' shoot biomasses and clipping decreased them. The two species' shoot biomasses were decreased significantly in the 3rd year compared with that in the 2nd year (Fig. 1). In d. nutans / F. /vina mixture, species' shoot biomass increased with fertilization and decreased with clipping and year treatments (Fig. 1). In F. sinensis / F. /vina mixture, species' shoot biomass increased with fertilization and decreased with clipping significantly (Fig. 1). The F. sinensis shoot biomass decreased in the 3rd year compared with the 2nd year. However, the F. /vina shoot biomass increased in the 3rd year (Fig. 1).

3.2. The relative c/mpetiti/n intensity

The ANOVA of three treatments on the Relative Competitive Intensity (RCI) in split-plots were as follows. For each of the species in each of the mixtures, there was significant effect for five of the six comparison between years (P<0.05), for one of the six comparison a highly significant effect of fertilisation (P<0.01). There were one instance each of first order interaction between fertiliser and year, and clipping and year. There were no significant third order interactions. In d. nutans / F. sinensis mixture, year had highly significant effects on the RCI of two species (P<0.01). Fertilization had highly significant effects on the RCI of F. sinensis. The interaction between fertilization and year had significant (P<0.05) effect on the RCI of d. nutans and the interaction between clipping and year had significant on that of F. sinensis. The RCI values of d. nutans were smaller than that of F. sinensis in all treatments (Fig. 2), which indicates that d. nutans is a superior competitor and F. sinensis is an inferior competitor in this mixture. In d. nutans / F. /vina mixture, year had highly significant (P<0.001) effect on the RCI of d. nutans and had significant (P<0.05) effect on that of F. /vina. The RCI values of d. nutans were all smaller than that of F.

ovina in all treatments, which indicated that d. nutans is superior to F. ovina (Fig. 2). In F. sinensis / F. ovina mixture, year had highly significant (P<0.001) effect on the RCI of F. sinensis. The RCI values showed that F. ovina was a superior competitor in all treatments in 3rd year (Fig. 2).

4. Discussion

In this experiment, the shoot biomass was greatest for dlymus nutans, then Festuca sinensis, and least for Festuca ovina in the 2nd year. However, in the 3rd year F. ovina, replaced F. sinensis. Some researches have shown that fertilization and clipping had large effects on plant growth [11-15]. We verified that fertilization and clipping had significant effects on species' shoot biomass in the 2nd and 3rd year of this experiment. Fertilization is a key management tool to improve species' shoot biomass yet clipping (simulating grazing) decreased it. This finding was also supported by other studies on the Qinghai-Tibetan Plateau [13-16].

Studies have shown that fertilization and clipping also affect competitive ability of species greatly [11-12]. However, this experiment showed that fertilization and clipping had no significant effect on the competitive ability according to the Relative Competitive Intensity (RCI) values of three species in two years except fertilization had significant effect on F. sinensis in the d. nutans / F. sinensis mixture. Although the RCI values for each species changed, the competitive hierarchy (according to the RCI values) did not change in the 2nd and 3rd year in spite of fertilization and clipping treatments. The result was consistent with those of Gu [16] and Gao [17]. They showed a consistent competitive hierarchy under different clipping intensities at different nitrogen levels (Artemisia frigida and Cleistogenes squarrosa in Gao's [17] study and three same species in Gu's [16] study). Thus clipping and fertilization had little effect on competitive pattern in mixtures on the Qinghai-Tibetan Plateau.

The competitive ability (according to the RCI values) was greatest for d. nutans, then F. sinensis, and followed F. ovina in the 2nd year. However, F. ovina surpassed F. sinensis in the 3rd year. Apparently, species' competitive hierarchy among species changed in over the two years. Many studies were conducted over only a single growing season even just a few weeks in one growing season [1]. However, competitive abilities of species can change [18]. So, short-term studies may lead to various conclusions on the overall competitive characteristics of species [19]. In this experiment, trial species experienced three years including seedling and adult growth. d. nutans was always a superior competitor in two mixtures in two growing seasons. F. ovina was an inferior competitor in two mixtures in the 2nd year but superior in the 3rd year. The results showed that species' competitive ability can change and is similar obtained in other studies [16,18].

In this experiment, F. sinensis and F. ovina were inferior competitors compared with d. nutans in mixtures regardless of fertilization and clipping treatments. This study showed that it is not feasible to use F. sinensis/F. ovina mixture in meadow development because of their low shoot biomasses. It also indicated that the mixtures of d. nutans / F. sinensis and d. nutans / F. ovina are better choice because of their higher shoot biomasses, which have potential to create a better agricultural production system. Figs

Fig 1. The shoot biomasses in three mixtures for three species of fertilization and clipping in 2nd and 3rd year. Error bars show the 95% CI of the means. The two-digit treatment codes on the y-axes refer to the six possible combinations of the two fertilizer (0- nil and 1- 900 kg ha-1)and three clipping (1- unclipped, 2- 60 mm residual height, 3- 20 mm residual height) treatments.

In d. nutans / F. sinensis mixture, black means F. sinensis shoot biomass and white means d. nutans shoot biomass. In d. nutans / F. /vina mixture, grey means F. /vina shoot biomass and write means d. nutans shoot biomass. In F. sinensis / F. /vina mixture, black means F. /vina shoot biomass and grey means F. sinensis shoot biomass.

F.sine nisi/E nutans

1112-' 13 -1 01 ■ 02 ■' 03-

F.ovina/E.nutans

F .sinenisi/E.nutans

12 13 01 02 03

- II—

FovinaiEnutans

Fcrvinafi7.sinensis

Relative Competition Intensity

Fig. 2 The relative competitive intensity in three mixtures for the three species across fertilization and clipping in 2nd and 3rd years. Error bars show the 95% CI of the means. The two-digit treatment codes on the y-axes refer to the six possible combinations of the two fertilizer (0- nil and 1- 900 kg ha-1)and three clipping (1- unclipped, 2- 60 mm residual height, 3- 20 mm residual height) treatments. In E. nutans / F. sinensis mixture, grey means F. sinensis RCI and white means E. nutans RCI. In E. nutans / F. ovina mixture, dark grey means F. ovina RCI and write means E. nutans RCI. In F. sinensis / F. ovina mixture, black means F. ovina RCI and grey means F. sinensis RCI.

Equation

RCI = (Pmono - Pmix) / Pmono

where Pmono represents the performance (expressed as tissue or biomass produced or as relative growth rate)of a plant in monoculture and Pmix represents the performance of a plant in mixture with the same density.

Acknowledgements

The study was financially supported by the Major State Basic Research Development Program of China (973 Program, 2009CB421308).

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