The Sown Biodiverse Permanent Pastures Rich in Legumes (SBPPRL) mix a large number of
species and cultivars of improved annual pasture species adapted to Mediterranean climate. with a
predominance of Trifolium subterraneum. On a commercial mixed farm were explored the effects of soil
microtopographic gradients on dry matter (OM) yields and species richness in two intensively grazed nearby
pastures - a stabilized SBPPRL and an old seminatural annual pasture (SNP) - established in the same
soil calena, with a high PZ05 and KzO availability. As expected the SBPPRL had higher DM yields than the
SNP, more stable along the slope system, and with a larger legume fraction. The indigenous genotypes of
the SNP seemed unable to translate into biomass soil fertility improvement. SBPPRL improved pasture
species depressed significantly pasture species diversity and species spatial turnover. In the SBPPRL
legumes mainly substituted many short living low productivity autochthonous species common in the SNP.
The buffering of soil ecological gradients is probably important in the explanation of the superior agronomic
performance of SBPPRL. SOM accumulation is certainly involved in this process

Aguiar, Carlos

Domingos, Tiago

Fernández-Núñez, E.

Pires, Jaime

Rodrigues, M.A.

Fernández-Núñez, Esther

Biblioteca Digital do IPB

New approaches for grassland research in a context of climate and socio-economic changes Edited by: Z. Acar, A. Lopez·Francos, C. Porqueddu OPTIONS mediterraneennes SERIES A: Mediterranean Seminars 2012 - Number 102 e CIHEAM The effect of soil microtopographic gradients on dry matter yields and species richness in two Mediterranean pastures C. Aguiar1*, M. Rodrigues\ M.E. Fernimdez-Nuriez1, T. Domingos2 and J. Pires1 lMountain Investigation Center (Cl MO), Instituto Politecnico de Bragan98, Apartado 1172, 5301-855 Bragan98 (Portugal) 20EM, and IN+, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal) *E-mail: cfaguiar@ipb.pt Abstract. The Sown Biodiverse Permanent Pastures Rich in Legumes (SBPPRL) mix a large number of species and cultivars of improved annual pasture species adapted to Mediterranean climate. with a predominance of Trifolium subterraneum. On a commercial mixed farm were explored the effects of soil microtopographic gradients on dry matter (OM) yields and species richness in two intensively grazed nearby pastures - a stabilized SBPPRL and an old seminatural annual pasture (SNP) - established in the same soil calena, with a high PZ05 and KzO availability. As expected the SBPPRL had higher DM yields than the SNP, more stable along the slope system, and with a larger legume fraction. The indigenous genotypes of the SNP seemed unable to translate into biomass soil fertility improvement. SBPPRL improved pasture species depressed significantly pasture species diversity and species spatial turnover. In the SBPPRL legumes mainly substituted many short living low productivity autochthonous species common in the SNP. The buffering of soil ecological gradients is probably important in the explanation of the superior agronomic performance of SBPPRL. SOM accumulation is certainly involved in this process. Keywords. Permanent pastures - Sown pastures - Subterranean clover - Species diversity. Effets des gradients microtopographiques du sol sur la production de matif�re seche et la diversite specifique sur deux paturages mediterraneennes Resume. Les Paturages Permanents Biodiverses Riclles en Legumineuses (PPBRL) melangent un nombre eleve d'especes et cultivars de plantes fourrageres ameliorees adaptees au climet mediterraneen, avec une preponderance de Trifolium subterraneum. Dans une exploration agricole on a explore I'effet de gradients microtopographiques sur fa production de matiere seche (MS), /a diversite specifique et le turnover d'especes dans deux paturages adjacents intensement broutes - /'un, (//1 PPBRL et I'autre un paturage seminaturel annuel (PSN) - instal/es dans la meme catena de sol avec niveaux de PzOs and K20 eleves. Comme if etait prevue, le PPBRL a montre des productions de MS plus hautes et plus stables au long du gradient microtopographique que le PSN, et une composante superiellre en legumil1euses. Les genotypes indigenes apparemment n'ont pas ete capables de convenir en biomasse /'ameJioralion de la fenilite du sol. Les especes ameliorees du PPBRL ont reduit significativement la diversite specifique, sunout d'especes annuel/es de cycle de vie coun, et le turnover spatial d'especes. L 'attenuation des gradienls eco/ogiques au nivaux du sol est probablement importante pour expliquer la performal1ce agronomique des PPBRL. La accumulation de matiere organique au sol est probabfemellt associee avec ce processus. Mots-cli�s. Pafurages permanents - Palurages semes - Tretle souterrain - Diversile de plantes. I - Introduction The Sown Biodiverse Permanent Pastures Rich in Legumes (SBPPRL) are a well known sown pastures system in many Mediterranean countries. Seed mixtures with a high species and cultivars diversity, with a predominance of Trifolium subterraneum, are their main characteristic. They often involve 10-12 improved cultivars of 6-7 pasture species with a Options Medilerrill1ffnnes, A, 110. 102, 2U 11 - Nelv approaches {or grassland research in Cl con/ex! of climafe and socio-economic changes 295 Mediterranean optimum, the majority of them self-regenerating winter annuals (only grasses are perennial). The SBPPRL address a classical subject in community ecology: the effects of species richness on ecosystem function. Recently we have been able to corroborate the hypotheses that SBPPRL species/cultivars richness track interannual climate fluctuations and slope system microenvironments arrays (Aguiar e/ al., 2011). Sown species and T. subterraneum cultivars richness are complementary in this process; they promote, respectively, interannual climatic fluctuations and rnicrotopographic gradients tracking. These abilities are central to explain the SBPPRL superior agronomic performances. Three hypotheses were tested in this article. 1) If SBPPRL's species and cultivars can track microtopographic ecological gradients, biomass yields should be higher in SBPPRL than in semi-natural pastures (SNP), in all slope positions. 2) In heterogeneous herbaceous plant communities the relationship between productivity and species richness generally follows a unimodal curb (Grime, 1973); consequently, if SBPPRL species inhabit soils with improved chemical fertility, and are substantially more productive than autochthonous biotypes, species richness at the local scale (alfa-diversity) is probably lower in SBPPRL than in SNP. 3) If a limited pool of improved species substitute indigenous species in fertilized soils, and SBPPRL's cultivar richness is fundamental in microtopographic ecological gradients tracking, then, species spatial turnover should be smaller in SBPPRL than in SNP. 11 - Materials and methods Two nearby pastures, a SNP and a SBPPRL, were selected on a private farm - Quinta da Fran,a (Covilhii, Portugal), 40'16'N7'30'W, ca.425m MSL. The SBPPRL was sown in arable land in 2001 with a commercial seed mixture. Since then it has been intensely grazed with cattle and sheep and annually fertilized with ca. 27 kg p,O, ha" . Grazing management led to a T. subterraneum absolute dominance; its sown grasses biomass is irrelevant. The SNP was also fertilized with phosphorous and intensively grazed, and wasn't yet invaded by SBPPRL genotypes. The studied pastures are located on a gentle slope of a granite hill with 30 m elevation and 380 m length. Three microtopographic positions were identified: hill shoulder, backslope and footslope. In the springs of 2008 and 2010 four quad rats were randomly located on each slope position. Each of the quad rats was protected with an exclosure cage three weeks before measurements to allow species identification. Species richness and relative cover was evaluated in the third week of May of 2008 and 2010, with the point-quadrat method (frame of 70x70 cm with 49 points). The 2009 spring was exceptionally dry and the pastures were impossible to sample. OM yields were evaluated in the agricultural year of 2007-2008 in exclosure cages around the previously described quadrats. Soil samples were collected nearby the quad rats of 2010. 2007-2008 and 2009-2010 agricultural years were, respectively, moderately dry (589 mm) and moderately wet (1023 mm). Temperature integrals in the two growing seasons were close to the mean year. Two explanatory variables were considered in the ANOVA analysis: SLOPE (three levels, Hill shoulder, Backslope and Footslope); and PTYPE (two levels, SBPPRL and SNP). In Ihe "within subject effects" ANOVA (Table 1) the YEAR explanatory variable (two levels, 2008 and 2010) was taken as repeated measures. The species turnover (beta diversity) was indirectly evaluated through the "Lengths of gradient" (Leps and Smilauer, 2003) available in the output of Oetrended Correspondence Analysis performed in the CANOCO program (T er Braak and Smilauer, 2002). The assessment of outcompeted species by the SBPPRL was done, indirectly, with a principal component analysis (PCA) ordination diagram with passively projected variables. Besides the variables used in the ANOVA, four new variables were created for the peA adding the relative cover of sown species (SOWN SPECIES), annual oligotrophic species (HELlANTHEMETEA GUTTATI), species adapted to trampled soils (POLYGONO-POETEA ANNUAE), and annual species of temporary wet soils (ISOETO-NANOJUNCETEA). The plant species autoecology was indirectly assessed through the phytosociological optimum (Rivas-Martinez et al., 2001). 296 Options Meri terr.1IU!CIJIlf!S, A, no. 1()2, 20 I! --III - Results and discussion Soil P,O, and K,O (mean 135 mg.kg·', Egner-Riehm) availability in the two studied pastures was elevated and �uite homogenous. Anyway, P,O, levels were significantly higher in the SNP (142 vs 90 mg.kg' , Egner-Riehm, p<0.001), and in backslope positions (mean 141 mg.kg"). Biomass yield was much higher in the SBPPRL, consequently, in spite of the cyclical soil disturbance that occurred before 2001, SOM content was significantly higher in this pasture type then in the SNP (2.76 vs 2.12%, p<0.001). In 2007,2008 the OM production was 250% higher in SBPPRL than in the SNP (6151 vs. 1752 OM kg.ha", p<0.001). PTYPE had a statistically significant effect in all OM yield fractions (grasses, legumes and others). In the SNP occurred a severe reduction of OM yields uphill: hill shoulder OM yield was almost an half (55.5%) of the footslope OM yield (1355 vs 2451 kg.ha", p<0.001). Inverselr SBPPRL had a much higher legumes content and proportion (3031 [49.3%] vs 248 kg.ha' [14.2%] in SNP, p<0.001), and buffered OM yields along the slope system (the SLOPE effect in total OM yield and in OM fractions of the SBPPRL was always insignificant). The higher grass biomass in the SBPPRL (1304 vs 681 kg.ha" in SNP) means tllat this yield fraction, almost only composed of indigenous plants, benefited from the legume presence. In Table 1, the between subjects (both years together) ANOVA shows that PTYPE and SLOPE had a significant effect on species richness. Species number per 0.49m-2 was higher in SNP (13.09 vs 10.56) and on hill shoulders (13.81 vrs. 10.38 and 11.31). The higher species richness in the hill shoulder was constant between years and between pasture types. In the within subject effects ANOVA only PTYPE effect was significant. In 2008, the SBPPRL had a higher species richness than the SNP (12.08 vs 11.25), but SNP had a much higher species richness peak in 2010 (14.92 vs 9.03) that explains its higher species richness in the between subject effect ANOVA. Table 1. Local species richness. AN OVA. Tukey's HSD test (P<O.05) Between subject effects PTYPE SBPPRL SNP SLOPE Meant 10.56 13.09 Hill shoulder 13.B1a Backslope 10.38b Footslope 11.31b 0.001 0.002 PTYPE X SLOPE 0.491 tNumber of species per 0.49m2, Error 5.319 5.319 5.319 Within subject effects Mean 2008t Mean 2010+ 1 2.08 9.03 11.25 14.92 14 13.63 10.63 10.13 10.38 12.25 p-value Error <0.001 5.847 0.318 5.847 0.935 5.847 The species turnover (beta,diversity) was much higher in the in SNP (DCA "Lengths of gradient" 3.791 in 2008 and 3.476 in 2010) then in SBPPRL (DCA "Lengths of gradient" 1.687 in 2008 and 1.733 in 2010). The first axe of the PCA diagrarn of Fig. 1 is correlated with the pasture types (r=0.80). The second axe probably reflects a water gradient; is highly correlated with ISOETO,NANOJUNCETEA (r= 0.93) and less with the year of sampling and the slope position. The direction of the ISOETO­NANOJUNCETEA arrow indicates that wet years and footslope positions promote temporary wet soils adapted species (e.g. T. cernuum). The PCA diagram also shows that sown species are a characteristic of SBPPRL, together with some undesirable nitrophilous species (e.g. Bromus hordeaceus and Sysimbrium officina/e) and of trampled soils plants. A large number of well fitted species inhabit the SNP. The majority of them are oligotrophic, ephemeral, annual plants New ,�pproachf's for grass/and research in cl context of climalf' <lIld �()ciO"'f'("onomit change'S 297 of the Helianthemetea guttati vegetation class. This phytosociological group is the most prone to be outcompeted by SBPPRL improved species. Aira caryophyllea, Logfia minima, To/pis barbata and Crassu/a til/aea, among other species, were not detected in the SBPPRL. o r"IJJ"""mI".·"'"'" !iKlSklPl ASBP?RL I!:t. HoU S" ..... ld'" o � "-1�.�O ---------------------- ---�1 . 5 Fig.1. peA biplot with the 20 species with the highest fit with the first two axes. IV - Conclusions The studied pastures shared similar soil chemical fertility conditions. Our experiment was based in pseudoreplications. Although the sampled agricultural years 2007-2008 and 2009-2010 represent climatic extremes, the number of studied years was small. Anyway, the gathered experimental data is congruent with the three hypotheses formulated in the introduction. The 2007-2008 total biomass yield, and its fractions, were higher in the SBPPRL than in the SNP, in all slope positions. The higher grass biomass in the SBPPRL means that this yield fraction, almost totally composed of indigenous species, was beneficiated by the legume presence. Nevertheless the indigenous pasture flora was unable to convert into biomass the improved fertility soil conditions, has SBPPRL legumes did. DM yield and its fractions variation along the slope system were buffered in the SBPPRL. This characteristic helps to explain the superior agronomic performance of the SBPPRL pasture system. SOM accumulation is certainly one of its causes. Species richness maxima occurred in SNP and in hill shoulder positions. SBPPRL improved pasture species outcompeted indigenous species - especially oligotrophic, ephemeral, unproductive annual plants - and depressed significantly pasture species richness. SBPPRL also reduced species turnover along the slope system. References Aguiar C., Pires J., Rodrigues M., Fernimdez-Nunz M.E. and Domingos T., 2011. The effects of climate fluctuations and soil heterogeneity on the f10ristic composition of sown Mediterranean annual pastures. In: Proceedings 16th Meeting of the FAO CIHEAM Mountain Pasture Network, Krak6w (Poland), p. 21-28. Grime J., 1973. Control of species richness in herbaceous vegetation. In: J. Environ. Managem., 1, p. 151-167. Leps I. and Smilauer P., 2003. Multivariate Analysis of Ecological Data using CANOCO. Cambridge University Press, Cambridge. Rivas-Martinez S., Fernimdez-Gonzalez F., Loidi J., Lousa M. and Penas A., 2001. Syntaxonomical checklist of vascular plant communities of Spain and Portugal to association level. In: ltinera Geabatanica, 14, p. 5-341. Ter Braak C. and Smilauer P., 2002. CANOCD Reference Manual and CanoDraw for Windows User's Guide (version 4.5). Microcomputer Power, lthaca. 298 Options Mediterraneennes, A, no. 102, 2012 ---

The effect of soil microtopographic gradients on dry matter yields and species richness in two Mediterranean pastures

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The effect of soil microtopographic gradients on dry matter yields and species richness in two Mediterranean pastures

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