The Impacts of Naturalized Legumes on Plant Communities in north Taiwan

摘要

過去研究顯示，入侵植物常對於當地的生物多樣性造成衝擊，包 括競爭排除、竭盡水源或改變微棲地物化性質等。其中，改變微棲地 物化性質往往造成深遠且不可逆的影響；然而，此環節卻鮮少被討論。

在眾多改變微棲地物化性質的機制中，固氮作用是最常見且能改變土 壤物化性質的重要機制之一。一般而言，豆科(Fabaceae)植物能藉由

固氮作用適應當地環境並增加該地區土壤的生物承載量，進而改變該 地區植物之生物量及多樣性。

本研究設立下列四個假說以探討歸化之豆科植物在北臺灣植物 群落之生物量及多樣性所造成之衝擊性：(1) 歸化豆科植物的存在與 相對較高的植物生物量及多樣性有關；(2) 歸化豆科植物提昇了土壤 含氮量；(3) 歸化豆科植物同時增加原生及外來植物之生物量及多樣 性；(4) 歸化豆科植物在不同棲地類型之植物群落造成之衝擊性會有 所不同。

實驗以北臺灣為樣區，利用每平方公里之網格系統，隨機選取

100 個 1km²樣區，利用正射化影像(Othophoto)判定棲地類型，並各

自選取五到十個不等的1m²小樣方，記錄GPS、海拔高度、棲地類型、

植物種類以及覆蓋度等，並轉換成多樣性指數包括Shannon(H’)、

Simpson(λ)、Pielou 均勻度指數(J)、Berger-Parker 優勢度指數(BP)、

物種數(S)及總覆蓋度(C)等六項指數；另外，收集土壤樣本以評估歸 化豆科植物之存在與否造成含氮量之差異性。

結果顯示，在100 km²中2242m²的小樣方共記錄了 16 種歸化豆 科植物，其中以大葛藤 (Pueraria lobata (Willd.) Ohwi ssp. thomsonii (Benth.) Ohashi & Tateishi)為最優勢之種類；大多數的歸化豆科植物為 原產於熱帶地區的草本，且偏好特定的棲地類型，如農地、河岸地、

荒廢地及路邊。在土壤營養鹽部份，歸化豆科植物提高了局部的氮總 量；另外，存在歸化豆科植物會顯著增加外來歸化植物之生物量及多 樣性，但對於原生植物卻沒有增加或減少的趨勢。然而，若將歸化豆 科植物從分析中移除，其存在與否對於其它外來歸化植物並沒有增加 或減少的趨勢。

此外，分別探討歸化豆科植物種數最多的五種棲地，包括荒廢地、

河岸、農地、墓地及路邊，其受衝擊程度與整體完全一致，即存在歸 化豆科植物會顯著增加這五種棲地類型之外來歸化植物生物量及多 樣性，但對於原生植物依舊沒有增加或減少的趨勢；但若將歸化豆科 植物從分析中移除，其存在與否亦對於這五種棲地類型之其它外來歸

化植物並沒有增加或減少的趨勢。

根據我們的結果，北臺灣地區之歸化豆科植物對於當地植物群落 生物量與多樣性之衝擊幾乎接近中性；然而，我們仍需密切注意歸化 豆科植物在臺灣中部與南部這些亞熱帶區域所造成之衝擊，一方面比 較改變棲地物化因子之相同分類群在不同緯度間之衝擊性必定是個 有趣的議題；另一方面，對於這些能改變棲地性質之分類群的了解能 更佳透徹。

關鍵字：入侵植物、歸化植物、衝擊、改變棲地者、豆科、固氮作用、

生物承載量、生物量、生物多樣性

ABSTRACT

It has been shown that invasive plants usually impact local biodiversity by competitive exclusion, water depletion, microhabitat transformation, etc. Among these impacts, nitrogen-fixation is one of the most serious transform mechanisms invasive plant, such as legumes, may employ. Although the impacts of invasive habitat transformer have been discussed in few studies, comprehensive approaches on the impacts of local biodiversity and biomass upon community level have yet been conducted. My main purpose of this study was to estimate the impacts of naturalized legumes, notorious habitat transformers, on local biomass and biodiversity.

To generate better understanding of the impacts caused by naturalized legumes on local plant communities, we developed and tested the following hypotheses: (1) Presence of naturalized legumes is associated with relatively higher biomass and biodiversity; (2) Presence of naturalized legumes elevates soil nitrogen; (3) Naturalized legumes increase local biomass and biodiversity of both native and naturalized species; (4) The impacts of naturalized legumes on local communities are varied along habitat types. Furthermore, we also anticipated answering the following questions: (1) What are the dominant naturalized legumes in the study areas? ; (2) What are the favorite habitat types of naturalized legumes?

The field investigation was carried out in four counties in north Taiwan. By using 1km² grid systems, one hundred of total grids were randomly selected as the sample areas. Five to ten square meters

quadrates; furthermore, were investigated. A total of 2,242 1-km² quadrats and twelve habitat types were recorded. Plant species and coverage of all native and naturalized species were collected, and IVI values were calculated for each naturalized legumes for the summary of dominance. Six biodiversity indices, including Shannon-Weaver (H’), Simpson (λ), Pielou evenness (J), Berger-Parker Dominance (BP) indices and species numbers (S), and total coverage (C) were summarized for further comparisons. In addition, soil samples were collected in pairs, presence and absence of naturalized legumes, to estimate the differences of available nitrogen.

A total of 629 species belonging to 130 families and 409 genus were documented. Among these species, 16 are naturalized legumes. Pueraria

lobata (Willd.) Ohwi ssp. thomsonii (Benth.) Ohashi & Tateishi was the

dominant species according to the IVI value, were recorded. Most of the naturalized legumes were herbs, from tropical areas, and preferred specific habitats, such as arable land, riparian, abandoned field, and roadside. In the part of soil nutrient, total nitrogen content was increased locally by naturalized legumes. Besides, local biomass and biodiversity of naturalized flora were increased significantly by naturalized legumes, but neither did native flora. However, the biomass and biodiversity of naturalized flora, excluding naturalized legumes, were not elevated on the enriched soils, either. Furthermore, separately for the habitat types, the results were consistently with overall condition that naturalized legumes significantly increased local biomass and biodiversity in those legume-preferred habitat types. But when naturalized legumes were

excluded, there were no significant difference in separate habitats, either.

According to our results, the impacts of naturalized legumes on local communities, including biomass and biodiversity, in north Taiwan were nearly neutral. However, we should still pay attention to naturalized legumes whose impacts on central and south Taiwan. On the one hand, comparisons of impacts of the same taxon of habitat transformers among different latitudes would be an interested issue; on the other hand, the comprehensive study for habitat transformers would be further clarified.

Key word: Invasive plant, Natulized plant, Impact, Habitat transformer, Fabaceae, Nitrogen fixation, Carry capacity, Biomass, Biodiversity

INTRODUCTION

The impacts of plant invasions on local plant communities have been documented worldwide, including biodiversity reduction, composition alternation, competitive exclusion, resource depletion, habitat transformation, etc (Vitousek & Walker, 1989; Vitousek, 1990;

Richardson et al., 2000b; Yoshida & Oka, 2004; Owens & Moore, 2007).

Among these impacts, habitat transformation has relatively profound effects, since abiotic and biotic components and interactions of local community may be modified consequently (Marr, 1993; Vitousek, 1994).

The commonest habitat transformation is usually performed by alien plant transformers, such as Betulaceae, Casuarinaceae, Coriariaceae, Datiscaceae, Elaeagnaceae, Fabaceae, Myricaceae, Rhamnaceae, Rosaceae, and Ulmaceae, through nitrogen-fixation (de Faria, et al., 1989;

Vitousek, 1990; Soltis, et al., 1995; Maron & Connors, 1996), and it often facilitates further invasions by naturalized species (Vitousek & Walker, 1989; Vitousek, 1990; Maron & Connors, 1996). The transformation of habitats starts with enriched soil following symbiosis of inhabited legumes and nitrogen-fixing bacteria and the process is irreversible (Paker & Paker, 2006). Consequently elevated local biomass and biodiversity following habitat transformation have been shown in many regions over the world (Vitousek & Walker, 1989; Vitousek, 1990; Maron

& Connors, 1996; Richardson et al., 2000a; Zahran, 2001; Haubensak &

Parker, 2004). Although elevated soil nitrogen may provide equal opportunities for both of native and naturalized species, introduced weeds are usually the beneficiaries of raising carry capacity due to their high

nutrient exploitation capacity (Huenneke, et al., 1990; Vitousek, 1990;

Marr, 1993; Vitousek, 1994; Maron & Connors, 1996). However, the effects of transformation to local plant community, including native and naturalized, were seldom discussed.

Fabaceae, the major plant group performing symbiosis with nitrogen fixing bacteria, is one of the most important plant families over the world and one of the largest contributors to the naturalized floras (Corlett, 1988;

Corlett, 1992; Pyšek, 1998; Pyšek et al., 2002; Wu et al., 2004a&b; Wu, unpublished) as well. It has been shown that about 84 % of Fabaceae performs symbiosis with nitrogen fixing bacteria, especially Papilionoideae (97%; de Faria, et al., 1989). Although reports on symbiosis of alien legumes and native nitrogen fixing bacteria are usually unavailable (Schlaepfer, et al., 2005; Reinhart & Callaway, 2006), root nodules of naturalized legumes are frequently seen in the fields according to our experiences.

The capacity of conducting symbiosis with nitrogen-fixing bacteria, the alien legumes usually naturalized in specific habitats, such as riverbank, roadside, etc (Wu, et al., 2005). These habitats equipped with high-frequency disturbance often facilitate dormancy breaking process via damaging the thick seed coats. It has been shown that nitrogen fixing bacteria usually effectuate nitrogen fixing mechanisms in habitats where soil nitrogen is relatively not available. The influences of naturalized legumes in different habitats, therefore, may be different in terms of increasing local biomass and biodiversity (Corlett, 1988; Corlett, 1992;

Williamson & Fitter, 1996; Zalba et al., 2000; Alston & Richardson,

2006; Morales & Aizen, 2006; Wu, 2006; Wu et al., submitted). For example, in poor-nutrient habitats, such as abandoned field, riparian, and roadside, are expectably more beneficial to naturalized legumes. In addition, there are also frequently high disturbance in the foregoing habitats, indigenous preference of high-disturbed habitats and possibly nutrient elevation via naturalized legumes are simultaneously contributed to exotic plant and accompany to serious invasion (Richardson, 2000a;

Alston & Richardson, 2006).

To generate better understanding of the impacts caused by naturalized legumes on local plant communities, we developed and tested the following hypotheses: (1) Presence of naturalized legumes is associated with relatively higher biomass and biodiversity; (2) Naturalized legumes increase local biomass and biodiversity of both native and naturalized species; (3) The impacts of naturalized legumes on local communities varied along habitat types (4) Presence of naturalized legumes elevates soil nitrogen content. Furthermore, we also anticipated answering the following questions: (1) What are the dominant naturalized legumes in the study areas? ; (2) What are the favorite habitat types of naturalized legumes?

在文檔中 北臺灣地區歸化豆科植物對於植物群落衝擊之研究 (頁 32-40)