Monika Krupa Native Grass Restoration May 8 2006p. 1Carbon addition in the Form of Sucrose and Sawdust as a Method of Restoring NativePerennial Grasses in Two Coastal California PrairiesMonika KrupaAbstract The extensive conversion of California’s grasslands into communities occupied byMediterranean annual grasses, and the nitrogen enrichment of areas in which native remnantpopulations still remain, have created a strong interest in employing labile carbon addition as amethod of restoring and preserving the native perennial bunchgrasses that once dominatedCalifornia’s landscape. Nitrogen enrichment has been shown to favor invasions of grasslands byannual species. Carbon addition to the soil may be used to temporarily decrease soil nitrogenavailability, which in turn may decrease the competitiveness of exotic annual grasses, andthereby give native seedlings a greater chance of survival. This study examined whether theaddition of labile carbon (in the form of sucrose and sawdust) reduced plant available nitrogenand increased native establishment in two coastal California prairies. In March 2006, sawdustand sucrose (400 g C/ m2) were added to plot that contained both native and exotic seedlings andmeasures of soil moisture and nitrogen levels were taken. I expect to find that carbon amendedplots have lower net nitrogen mineralization and nitrification rates and lower ammonium andnitrate concentrations than umamended plots. At both sites, there was no significant differencein soil moisture levels between the two treatments. This implies that any differences in speciescomposition can be attributed to differences in soil nitrogen levels rather than differences in soilmoisture.Monika Krupa Native Grass Restoration May 8 2006p. 2IntroductionInvasions by exotic species have been acknowledged as critical components of human-induced ecosystem change and pose a serious threat to global biodiversity (Mack et al. 2000,Borer et al. 2003, Corbin and D’Antonio 2004). The transformation of nearly all of the 10million hectares of California grasslands from native perennial bunchgrass communities intoannual Mediterranean grass communities is one of the most dramatic examples of a large-scaleinvasion in the world (Corbin et al. 2004, Borer et al. 2003). There are currently many ongoingattempts to restore native California bunchgrasses to grasslands that are dominated by annualexotic species (Corbin et al. 2004).Among the methods being tested is the lowering of soil nitrogen (N) levels through theaddition of organic carbon (C), most often in the form of sucrose and/or sawdust, to the soil(Zink and Allen 1998, Reever Morghan and Seastedt 1999, Torok et al. 2000, Cione et al. 2002,Blumenthal et al. 2003, Averett et al. 2004, Corbin et al. 2004). Today, the spread of invasive N-fixing species into many ecosystems around the world (Vitousek et al. 1987, Maron and Connors1996, Maron and Jefferies 1999, Mack et al. 2000, Corbin et al. 2004) combined with the impactof human activities, such as the use of nitrogen fertilizer, fossil fuel combustion, the planting ofN-fixing crops in agriculture, and the mobilization of N from long-term biological storage pools(Vitousek et al. 1997, Bobbink et al. 1998, Corbin et al. 2004), have caused a large increase inthe amount of N available for use by species in all environments.Historically, N has been a limiting nutrient in most ecosystems, and native species in thesesystems are adapted to these low N conditions (Vitousek et al. 1997, Blumenthal et al. 2003). Incontrast, many invasive species have a life strategy of growing quickly and producing largeamounts of seed. This strategy is dependent on the wide availability of N (Huenneke et al. 1990,McLendon and Redente 1992, Rothrock and Squiers 2003). When the pool of available Ndecreases, these species lose their competitive advantage, and native species, which areaccustomed to competing for N, are better able to compete against the invaders (McLendon andRedente 1992, Blumenthal et al. 2003, Rothrock and Squiers 2003). Higher available soil N inmany ecosystems, including grasslands, has consequently been found to promote and sustain thepresence of invasive weeds (Huenneke et al. 1990, McLendon and Redente 1992, Redente et al.1992, Maron and Connors 1996, Vitousek et al. 1997, Bobbink et al. 1998, Maron and Jefferies1999, Paschke et al. 2000, Rothrock and Squiers 2003, Corbin et al. 2004), and recent researchMonika Krupa Native Grass Restoration May 8 2006p. 3indicates that lowering levels of soil N can shift the community composition back towards nativespecies (Zink and Allen 1998, Blumenthal et al. 2003, Averett et al. 2004).Studies have shown that soil N levels can be lowered through the addition of organic C intothe soil, which stimulates soil microbe immobilization of N (Killham 1994, Corbeels et al. 2000).This decreases the amount of ammonium and nitrate available to plants and thereby lowers plantgrowth (Reever Morghan and Seastedt 1999, Blumenthal et al. 2003, Averett et al. 2004, Corbinet al. 2004). Although both native and exotic growth decreases with C addition, it is expectedthat native species will be better able to compete against nitrophilic exotics in lower N conditions(Corbin et al. 2004). The results of experiments on the effects of C addition on soil Navailability and plant growth have varied however (Zink and Allen 1998, Reever Morghan andSeastedt 1999, Cione et al. 2002, Blumenthal et al. 2003, Averett et al. 2004, Corbin andD’Antonio 2004), and this area needs further investigation.Because the effects of C addition are temporary, repeated additions of C to the soil over thecourse of a year influence community composition more strongly then the application of only asingle treatment (Morghan and Seastedt 1999, Torok et al. 2000, Cione et al. 2002). Theapplication of C in the spring, during the peak growing season, is especially important becausethis is the time period in which plants take up the most nutrients (Morghan and Seastedt 1999,Cione et al. 2002). Sucrose supplies a large amount C in a form that is readily exploited bymicrobes, so its effects are seen more quickly, but they last for a shorter period of time then theeffects of sawdust addition (Torok et al. 2000). Sawdust supplies C in a form that must bebroken down, and it is therefore not as quickly utilized by microbes, but its effects on soil N lastlonger then the effects of sucrose addition (Torok et al.
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