Appendix A. Individual Conceptual Networks Representing Agricultural Management and Ecosystem

1Appendix A. Individual conceptual networks representing agricultural

2management and ecosystem services provision.

4 The relationships between agricultural management and eight ecosystem

5services (ES) provided by Pampean agroecosystems were represented in individual

6conceptual networks (Figs. 1 to 8). The eight conceptual networks developed in this

7work contained five types of nodes, and four types of logical links between nodes (see

8Section 2.3.). These logical links present capital letters in order to easily explain each

9conceptual network.

111. Supporting Service: Elements cycling - C Balance

13Fig. 1 Conceptual network representing functional relationships between agricultural management and

14provision of the Supporting service: Elements cycling - C balance. Capital letters represent the logical

15links between nodes. Legend: circles meaning input variables; rounded-squares meaning decision

16variables; squares meaning state variables; triangles meaning ecosystem processes and diamond meaning

17ecosystem service provision indicators. Tº: temperature, and Pp: rainfall

1 1 19 It is generally known that C inputs in soils consist of crop residues and roots,

20and sometimes additions of soil organic amendments; while C loss is caused by humus

21and residue mineralization, in conditions where soil erosion and C leaching are minimal

22(C leaching is not an important cause of soil organic carbon (SOC) losses in Pampean

23agroecosystems (Roberto Álvarez, personal communication)) (Oorts and others 2006).

24The interaction between temperature and rainfall regulates SOC through the influence

25of soil organic matter (SOM) mineralization (Fig. 1, Relations A and B) (Roberto

26Álvarez and Raúl Lavado, personal communication). High temperature reduces SOC

27because of intense SOM mineralization, while there is no linear answer for rainfall (Fig.

281, Relations A, B and F) (Álvarez and Lavado 1998). However, it is widely accepted

29that, in general, rainfall has the same effect as temperature (Fig. 1, Relations B and F)

30(Roberto Álvarez and Raúl Lavado, personal communication). Additionally, crop

31species, their growth rate and yield determine the amount and type (i.e., quality) of crop

32residue (including crop roots) (Fig. 1, Relations D and I) (Ernst and others 2002) which

33change SOC in surface soil layers, specially in no-tillage systems (Álvarez and Lavado

341998). Surface soil layers have greater C amounts because of the input of crop residue

35from harvested plants (Álvarez and Lavado 1998). Generally, legume species (e.g.,

36soybean) have higher mineralization rates than gramineous species (e.g., wheat, maize)

37due to lower C/N relations (Fig. 1, Relation E) (Ernst and others 2002).

38 Another conditioning factor of SOC reduction is erosion vulnerability which is

39higher in continuous cropping systems, principally by 1) removing C from one site and

40depositing it elsewhere, and 2) promoting soil degradation and then reducing

41productivity (Fig. 1, Relation G) (Martínez-Mena and others 2008). However, it can be

42assumed that SOC movement is dependent on the topographic position (Haydée

43Steinbach and Roberto Álvarez, personal communication). Soils under no-tillage reduce

2 2 44both eolic erosion in semiarid sites, and hydric erosion in sites with great slopes

45(Monzon and others 2006).

472. Supporting Service: Elements cycling - N Balance

50provision of the Supporting service: Elements cycling - N balance. Capital letters represent the logical

52variables; squares meaning state variables; triangles meaning ecosystem processes and diamond meaning

53ecosystem service provision indicator. Tº: temperature, and Pp: rainfall

54 55 Soil nitrogen (N) availability is modulated by four main factors: SOM

56mineralization, crop residue, fertilization regime and N losses (Cassman and others

572002). N mineralization through SOM is a very important supply source due to its usage

58availability (Fig. 2, Relation G), increasing or decreasing crop yield (Fig. 2, Relation J)

59(Bono and Álvarez 2007). The increase in soil moisture content increases mineralized N

60(Fig. 2, Relations B and F) (Helena Rimski-Korsakov, personal communication). This

61increase is a direct consequence of higher microbial activity, until the concentration of

3 3 62oxygen in the soil becomes a limitation for the microorganisms (Navarro and others

631991). Moreover, SOM is not only affected by mineralization but also by crop residue

64disposal on soil surface layers (Fig. 2, Relation E) (Ernst and others 2002), as it occurs

65for SOC in no- and reduced tillage systems. N fertilization can increase the amount of

66soil N pools which will be available for crops (Fig. 2, Relation K) (Abril and others

672007). However, N excedent can also be immobilized by microorganisms, resulting in a

68non linear effect (i.e., increase or reduce) of the application (Fig. 2, Relation K)

69(Cassman and others 2002; Portela and others 2006). Furthermore, N losses by

70denitrification, volatilization or leaching are the main causes for the low efficiency in

71the use of N, and therefore they affect available N in soil (Fig. 2, Relation L) (Abril and

72others 2007). Because of the low degree of these losses during the whole crop growth

73cycle (Álvarez and Grigera 2005), they can be grouped all together under the name of N

74losses (Roberto Álvarez, personal communication).

763. Supporting Service: Water cycling - Soil water balance

79provision of the Supporting service: Water cycling - Soil water balance. Capital letters represent the

80logical links between nodes. Legend: circles meaning input variables; rounded-squares meaning decision

81variables; squares meaning state variables; triangles meaning ecosystem processes and diamonds meaning

82ecosystem service provision indicators. Tº: temperature, and Pp: rainfall

4 4 83 84 In Pampean agroecosystems, water supply for crops is determined by nine

85variables: 1) evaporation, 2) runoff, 3) soil structural stability, 4) soil texture, 5) aquifer

86depth, 6) soil depth, 7) presence of weeds/fallow/cover crops, 8) irrigation, and 9)

87rainfall (Fig. 3, Relations M, N, O, P, Q, R, S, T and C). These variables, in general,

88increase or affect water supply for crops. For instance, no-tillage systems leave crop

89residue on the soil surface and, therefore, soil evaporation is clearly decreased (Fig. 3,

90Relations E and F) (Monzon and others 2006). Relative soil evaporation rates directly

91influence the amount of soil water retained which will be used by the crop (Fig. 3,

92Relation M) (O´Leary and Connor 1997). Stubble mulch protects the surface soil from

93erosion and runoff, and increases water storage by minimising surface sealing and

94enhancing infiltration, as well as by directly reducing evaporation (Fig. 3, Relations G,

95J, N and O) (O´Leary and Connor 1997). Moreover, irrigation not only increases water

96supply for crops (Fig. 3, Relation T) but also affects runoff, depending on the amount of

97water irrigated and crop residue on soil surface (Fig. 3, Relation L) (Olga Heredia,

98personal communication). Systems under no-tillage can increase soil water

99accumulation during fallows (Fig. 3, Relation S), and thereby offer the potential for

100affecting crop yield in Pampean agroecosystems (Olga Heredia and Francisco Bedmar,

101personal communication) (Fig. 3, Relation U).

102 Soil depth is related with the ability of roots to explore soil profile and to absorb

103water stored there (Fig. 3, Relation R); on the other hand, aquifer depth can be defined

104by characterizing the average depth fluctuation of water table in different regions (Fig.

1053, Relation Q) (Esteban Jobbágy, personal communication). This is specially important

106in sandy soils (Claudia Sainato, personal communication). Finally, weeds can be burned

107to avoid evaporation as well as the establishment of cover crops (Fig. 3, Relation S)

108(Olga Heredia and Silvina Portela, personal communication).

5 5 109

1104. Supporting service: Soil conservation – Soil structural maintenance

113provision of the Supporting service: Soil conservation – Soil structural maintenance. Capital letters

114represent the logical links between nodes. Legend: circles meaning input variables; rounded-squares

115meaning decision variables; squares meaning state variables; triangles meaning ecosystem processes and

116diamonds meaning ecosystem service provision indicators. Tº: temperature, and Pp: rainfall

117 118 Structural stability is defined as soil capacity to preserve the system of solids and

119pore space, when subjected to different external disturbances (e.g., tillage) (Taboada

120and Micucci 2002). Its loss is the critical factor which determines structural

121deterioration. This deterioration is evidenced by the formation of surface crusts, higher

122rates of runoff and soil loss due to erosion, as well as reduced water storage (Taboada

123and Micucci 2002). Soil structural stability is clearly affected by land use, which is in

124turn positively associated with crop residue, total organic C concentration and the forms

125of organic C (Fig. 4, Relations I and J) (Caravaca and others 2004). The close

126association found between structural stability, labile carbon and microbial biomass

6 6 127confirms both their importance in the mineralization process and their ability as

128aggregate cementitious (Fig. 4, Relations G and H) (Urricarriet and Lavado 1999).

129According to the first statement, SOM decomposition may be limited by pore size

130distribution due to the localization of SOM in pores inaccesible to microorganisms, a

131limited nutrient supply to microorganisms and restricted predation of those

132microorganisms (Miguel Taboada and Roberto Casas, personal communication).

133Furthermore, soil structural stability is one of the most important characteristics

134affecting crop yield (Fig. 4, Relation K) because it affects root penetration, water

135storage capacity, and air and water movement in soil (Fig. 4, Relation O) (Aparicio and

136Costa 2007).

1385. Regulating Service: Climate regulation – N2O emission control

141provision of the Regulating service: Climate regulation – N2O emission control. Capital letters represent

142the logical links between nodes. Legend: circles meaning input variables; rounded-squares meaning

143decision variables; squares meaning state variables; triangles meaning ecosystem processes and diamonds

144meaning ecosystem service provision indicators. Tº: temperature, and Pp: rainfall

7 7 146 Although denitrification is only part of direct N2O emissions from soils, it is the

147most studied process in contrast with nitrification occurring in unsaturated soils, among

148other conditions (Fig. 5, Relation P) (Laura Yahdjian, personal communication). Thus,

149the main factors controlling denitrification are: soil pH, soil texture, nitrate

150concentration, C availability, aeration and moisture content (Guo and Zhou 2007).

151However, the major factors to consider, in terms of N2O production in Pampean

152agroecosystems, are available N in soil and moisture content (in this case, rainfall) (Fig.

1535, Relations N and O) (Palma and others 1997; Ciampitti and others 2005). For instance,

154it is known that the presence of actively growing plants limits the denitrification process

155in comparison with those treatments without plants, due to reduced water availability

156and to lower levels of nitrates in soil, to a lesser extent (Sainz Rozas and others 2004).

157Once the crop is harvested and crop residue remains on the surface, soluble C

158concentration is associated with denitrification (Fig. 5, Relation E); this is because

159bacteria biomass capable of denitrification is probably controlled primarily by C

160availability under aerobic conditions (Fig. 5, Relation M) (Miguel Taboada, personal

161communication), while emissions occur mainly during anaerobic conditions (Fig. 5,

162Relation O).

1646. Regulating Service: Water purification - Groundwater contamination control

8 8 166Fig. 6 Conceptual network representing functional relationships between agricultural management and

167provision of the Regulating service: Water purification - Groundwater contamination control. Capital

168letters represent the logical links between nodes. Legend: circles meaning input variables; rounded-

169squares meaning decision variables; squares meaning state variables; triangles meaning ecosystem

170processes and diamonds meaning ecosystem service provision indicators. Tº: temperature, and Pp: rainfall

172 Nitrate (NO3) leaching is one of the main causes for groundwater contamination

173(Fig. 6, Relations N and O) (Abril and others 2007; Claudia Sainato and Olga Heredia,

174personal communication). However, Mugni and others (2005) measured NO3

175concentration in four Pampasic streams and concluded that it was relatively modest

176compared to intensively cultivated basins in Europe and North America. Consequently,

177there is a slow N enrichment of water resources in Pampean agroecosystems (Portela

178and others 2006). Water quality is reduced not only by N fertilization (Fig. 6, Relation

179J) (Rimski-Korsakov and others 2004; Abril and others 2007), but also SOM

180mineralization through several years removes great amounts of NO3 towards aquifers

181(Portela and others 2006; Helena Rimski-Korsakov and Raúl Lavado, personal

182communication) (Fig. 6, Relation G). N fertilization could also be indirectly inducing

183soil NO3 leaching, by altering the ability of plants root system to acquire N from soil

184and net mineralization rate from organic N pools (Cassman and others 2002).

185Furthermore, fertilization in excess of crop requirements or water excedent, such as

186rainfall events (Fig. 6, Relation M) or irrigation (Fig. 6, Relation K), increase the

187probability of soil NO3 leaching (Costa and others 2002; Rimski-Korsakov and others

1882004; Vergé and others 2007). It is important to clarify that the Pampa region has low N

189inputs through rainfall (Portela and others 2006). Other factors affecting soil NO3

190leaching are particle size distribution, soil porosity and the ocurrence of preferential

191flow paths. These causes can be grouped under soil texture, which is another important

9 9 192factor because of its ability for retaining water (Fig. 6, Relation L) (Taboada and

193Micucci 2002).

1957. Regulating Service: Regulation of biotic adversities

198provision of the Regulating service: Regulation of biotic adversities. Capital letters represent the logical

200variables; squares meaning state variables; triangles meaning ecosystem processes and diamonds meaning

201ecosystem service provision indicators

203 In Pampean agroecosystems, crop environment is determined by: 1) tillage

204system, 2) crop protection, 3) sowing density, 4) sowing date, 5) fertilization, 6)

205genotype selection, and 7) irrigation (Fig. 7, Relations B, A, C, D, E, F and G). These

206variables affect not only crop yield but also species composition and abundance of plant

207and animal community, and beneficial species (Fig. 7, Relations H, J and L) (Emilio

208Satorre and Elba De la Fuente, personal communication). Beneficial species as well as

209crop environment and crop changes affect species composition and

210abundance/incidence of pests, diseases and weeds (Fig. 7, Relations K, L and N). The

211latter reduces crop yield and affects natural pest mitigation of ecosystems (Fig. 7,

10 10 212Relations I and O). The presence of weeds influences the presence of diseases and

213diversity and abundance of two insect types: pests, with negative consequences for

214cropping systems, and their natural enemies (Altieri 1999). Generally, a high density of

215weeds is counter-productive because they reduce crop yield and its quality (Albrecht

2162003).

2188. Biodiversity maintenance

221Biodiversity maintenance. Capital letters represent the logical links between nodes. Legend: circles

222meaning input variables; rounded-squares meaning decision variables; squares meaning state variables;

223triangles meaning ecosystem processes and diamond meaning ecosystem service provision indicator

225 Biological diversity or biodiversity is defined as the wide variety of plants,

226animals, microorganisms and their genetic variations (Altieri 1999). In agroecosystems,

227the variety of crops are also considered as biodiversity components (María Elena

228Zaccagnini, personal communication). However, the type and abundance of biodiversity

229may differ across agroecosystems in relation to their crop protection (i.e.,

11 11 230phytotherapics application) and tillage system (Fig. 8, Relations A, B and C) (María

231Elena Zaccagnini, personal communication).

232 Other management strategies for increasing biodiversity involve the 1)

233manipulation of undisturbed areas within agroecosystems, 2) preservation of weeds, or

2343) introduction of mixtures containing grasses, legumes, flowering and/or aromatic

235plants. These strategies offer alternative food sources (i.e., pollen, nectar) to different

236organisms, and places for hibernation and reproduction (Fig. 8, Relation D) (Carmona

237and Landis 1999; Carmona and others 1999; Landis and others 2000). Furthermore,

238areas functioning as shelters act as biological corridors in the mobility of natural

239enemies (decreasing, in some cases, phytotherapic application) and their non-

240fragmentation is fundamental to the establishment of these organisms and the rapid

241recolonization of agroecosystems after a disturbance (Fig. 8, Relation D) (Carmona and

242Landis 1999; Landis and others 2000; Jonsson and others 2008; Gardiner and others

2432009; Rufus and others 2009).

244 Sequences, rotations and landscape structure provide two types of

245agroecosystems heterogeneity (Fig. 8, Relations E and F). On the one hand,

246sequences/rotations are recognized as temporal heterogeneity even though they are

247planned biodiversity (e.g., crops, pastures); on the other hand, landscape structure can

248be identified as spatial heterogeneity (Elba De la Fuente, personal communication).

249Landscape structure plays a crucial role in the survival of species by offering different

250kinds of habitat (Claudio Ghersa, personal communication).

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