Monika Krupa Native Grass Restoration May 8 2006 Carbon addition in the Form of Sucrose and Sawdust as a Method of Restoring Native Perennial Grasses in Two Coastal California Prairies Monika Krupa Abstract The extensive conversion of California s grasslands into communities occupied by Mediterranean annual grasses and the nitrogen enrichment of areas in which native remnant populations still remain have created a strong interest in employing labile carbon addition as a method of restoring and preserving the native perennial bunchgrasses that once dominated California s landscape Nitrogen enrichment has been shown to favor invasions of grasslands by annual species Carbon addition to the soil may be used to temporarily decrease soil nitrogen availability which in turn may decrease the competitiveness of exotic annual grasses and thereby give native seedlings a greater chance of survival This study examined whether the addition of labile carbon in the form of sucrose and sawdust reduced plant available nitrogen and increased native establishment in two coastal California prairies In March 2006 sawdust and sucrose 400 g C m2 were added to plot that contained both native and exotic seedlings and measures of soil moisture and nitrogen levels were taken I expect to find that carbon amended plots have lower net nitrogen mineralization and nitrification rates and lower ammonium and nitrate concentrations than umamended plots At both sites there was no significant difference in soil moisture levels between the two treatments This implies that any differences in species composition can be attributed to differences in soil nitrogen levels rather than differences in soil moisture p 1 Monika Krupa Native Grass Restoration May 8 2006 Introduction Invasions by exotic species have been acknowledged as critical components of humaninduced 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 10 million hectares of California grasslands from native perennial bunchgrass communities into annual Mediterranean grass communities is one of the most dramatic examples of a large scale invasion in the world Corbin et al 2004 Borer et al 2003 There are currently many ongoing attempts to restore native California bunchgrasses to grasslands that are dominated by annual exotic species Corbin et al 2004 Among the methods being tested is the lowering of soil nitrogen N levels through the addition 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 Nfixing species into many ecosystems around the world Vitousek et al 1987 Maron and Connors 1996 Maron and Jefferies 1999 Mack et al 2000 Corbin et al 2004 combined with the impact of human activities such as the use of nitrogen fertilizer fossil fuel combustion the planting of N 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 in the 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 these systems are adapted to these low N conditions Vitousek et al 1997 Blumenthal et al 2003 In contrast many invasive species have a life strategy of growing quickly and producing large amounts 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 N decreases these species lose their competitive advantage and native species which are accustomed to competing for N are better able to compete against the invaders McLendon and Redente 1992 Blumenthal et al 2003 Rothrock and Squiers 2003 Higher available soil N in many ecosystems including grasslands has consequently been found to promote and sustain the presence 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 Jefferies 1999 Paschke et al 2000 Rothrock and Squiers 2003 Corbin et al 2004 and recent research p 2 Monika Krupa Native Grass Restoration May 8 2006 indicates that lowering levels of soil N can shift the community composition back towards native species 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 into the 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 plant growth Reever Morghan and Seastedt 1999 Blumenthal et al 2003 Averett et al 2004 Corbin et al 2004 Although both native and exotic growth decreases with C addition it is expected that 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 N availability and plant growth have varied however Zink and Allen 1998 Reever Morghan and Seastedt 1999 Cione et al 2002 Blumenthal et al 2003 Averett et al 2004 Corbin and D Antonio 2004 and this area needs further investigation Because the effects of C addition are temporary repeated additions of C to the soil over the course of a year influence community composition more strongly then the application of only a single treatment Morghan and Seastedt 1999 Torok et al 2000 Cione et al 2002 The application of C in the spring during the peak growing season is especially important because this 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 by microbes so its effects are seen more quickly but they last for a shorter period of time then the effects of sawdust addition Torok et al 2000 Sawdust supplies C in a form that must be broken down and it is therefore not as quickly utilized by microbes but its effects on soil N last longer then the effects of sucrose addition Torok et al 2000 Many studies incorporate the use of both sucrose and sawdust in their treatments as a way of generating a quick and long lasting effect on soil N
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