Effects of nutrient addition and acidification on plant species diversity and seed germination in heathland

Abstract

Summary1. The atmospheric deposition of sulphur and nitrogen compounds in the Netherlands has been responsible for decreasing plant species diversity in heathland. To unravel the relative importance of nitrogen compounds on soil acidification and eutrophication, and hence on the vegetation, we carried out a factorial addition experiment and a germination experiment in heathland on nutrient-poor sandy soil. 2. We changed nutrient availability and acidity independently in eight different treatments that, respectively, added nutrients or carbon in various combinations (N, P, glucose) or added acidifying or neutralizing compounds. One treatment also involved adding Al. Additions occurred five times per year during 5 years, in an area from which sods had been removed before the experiment began. The same design was used for the germination experiment, but the treatments were applied for 2 years. 3. Our results showed that acidification was the most important factor in reducing species diversity. In addition, the germination of several heathland species was significantly reduced in plots with a pH below 5, and germination was very poor in plots where Al had been added. 4. The number of plant species declined particularly with increasing Al in the upper soil horizons. We conclude that this relationship is responsible for the influence of acidification on plant species richness in heathland. 5. The influence of nutrient availability on species composition in heathland was subsidiary to acidity, but nutrient availability influenced species composition in an independent way. The growth of the three dominant species ( Molinia caerulea , Calluna vulgaris and Erica tetralix ) was limited by different nutrients. Erica tetralix was limited by N, Calluna vulgaris by P and Molinia caerulea by both N and P. We argue that increased N availability will change the relative availability of N and P, which can decrease species diversity. 6. Together these results show how factorial experiments can elucidate the complex ecological effects arising from sulphur and nitrogen deposition, revealing different mechanisms that change species richness and community composition.

Long-term nitrogen deposition depletes grassland seed banks

“…It may also be that the Blue dashed lines show alternative mechanisms of seed bank depletion based on the species-specific effects of N pollution on seeds (not discussed above). N-containing compounds, soil acidification and phytotoxic metals may have a negative 21,22,43,44 or neutral 22,44 effect on germination, and therefore can increase the size of the seed bank through increased seed dormancy. Greater seed availability to microorganisms can then increase seed mortality with time.…”

Testing mechanisms of N-enrichment-induced species loss in a semiarid Inner Mongolia grassland: critical thresholds and implications for long-term ecosystem responses

“…N addition increases primary production and hence causes cascading effects on competitive exclusion including assemblage thinning [7,18], the relative importance of above-ground or light competition over below-ground competition [19,20] and reduction of species recruitment [21,22]. For some systems, N addition increases soil acidity and results in toxicity through mobilization of metals, leaching of base cations and changing the balance between nitrogenous compounds [23][24][25]. After decades of efforts, however, there are few agreements but, rather, results are case-dependent [4,10,17] or even opposite of expectations [26].…”

Effects of nutrient addition and soil drainage on germination of N-fixing and non-N-fixing tropical dry forest tree species

“…The role of N addition in reducing seed germination has also been proposed as a control measure for agricultural weeds (Pesch and Pieterse 1982;Dzomeku and Murdoch 2007) and parasitic plants (Irmaileh 1994). On the other hand, a number of studies have also reported no change in germination proportion with nutrient addition (Broncano et al 1998;Roem et al 2002), as well as stimulation, resulting in an increase in germination (Benech-Arnold et al 2000;Plassmann et al 2008).…”

“…As a considerable fraction of a seed's mass is made up of stored carbohydrate and nutrient reserves (Fenner and Thompson 2005), it can be argued that the availability of nutrients in the germination media or environment may have only a minimal effect, if any on germination success (e.g. Broncano et al 1998;Roem et al 2002). However, studies have shown that N and P addition can influence seed germination.…”

“…Therefore, assessing the effects of nutrient deposition on the early post-reproductive stages of plants, such as germination, is important in quantifying the mid-to long-term impacts of N and P deposition on ecosystems (Ackerly and Bazzaz 1995;Callahan et al 2008). Although water availability (Khurana and Singh 2004;Renzhong and Qiong 2004;Ronnenberg et al 2008), temperature (Ronnenberg et al 2008;Milbau et al 2009), soil properties (Roem et al 2002) and the intensity, as well as quality of available light (Metcalfe 1996;Broncano et al 1998;Holl et al 2000;Ceccon et al 2003;Luna and Moreno 2009), are all well recognised as important determinants of germination success, the role of nutrient availability remains poorly quantified. As a considerable fraction of a seed's mass is made up of stored carbohydrate and nutrient reserves (Fenner and Thompson 2005), it can be argued that the availability of nutrients in the germination media or environment may have only a minimal effect, if any on germination success (e.g.…”