Table 3.
Summary of mixed-effects model analyses for functional traits combining all grass species
| Relative height |
Stem mass fraction |
Shoot length |
Specific leaf area |
Leaf length |
Internode length |
Leaf nitrogen |
Biomas s : N ratio |
Foliar δ15N |
Foliar δ13C |
|||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| L ratio | P | L ratio | P | L ratio | P | L ratio | P | L ratio | P | L ratio | P | L ratio | P | L ratio | P | L ratio | P | L ratio | P | |
| (A) Species richness prior to functional group composition | ||||||||||||||||||||
| SR | 5·15 | * ↓ | 4·77 | * ↑ | 5·98 | * ↑ | 6·93 | ** ↑ | 3·55 | 0·91 | 0·62 | 2·99 | . | 29·62 | *** ↓ | 28·39 | *** ↓ | |||
| LEG | 7·77 | ** ↓ | 4·90 | * ↑ | 6·83 | ** ↑ | 26·44 | *** ↑ | 9·89 | ** ↑ | 0·57 | 6·83 | ** ↑ | 6·92 | ** ↓ | 0·17 | 5·19 | * ↓ | ||
| SHERB | 0·13 | 0·05 | 0·02 | 0·08 | 0·10 | 1·95 | 1·02 | 0·05 | 0·79 | 2·13 | ||||||||||
| THERB | 0·31 | 0·99 | 0·25 | 1·39 | 2·56 | 1·23 | 0·13 | <0·01 | 0·34 | 3·59 | ||||||||||
| ID | 80·37 | *** | 209·39 | *** | 252·62 | *** | 165·00 | *** | 204·82 | *** | 134·65 | *** | 37·87 | *** | 29·08 | ** | 27·02 | ** | 155·67 | *** |
| ID × SR | 25·46 | ** | 22·36 | * | 26·72 | * | 20·65 | * | 35·16 | *** | 32·95 | *** | 15·75 | 28·71 | ** | 20·66 | * | 55·66 | *** | |
| ID × LEG | 8·63 | 12·03 | 17·19 | 21·09 | * | 28·86 | *** | 26·43 | ** | 27·39 | ** | 25·11 | ** | 40·92 | *** | 30·51 | ** | |||
| ID × SHERB | 21·87 | * | 13·52 | 14·06 | 13·63 | 15·88 | 32·63 | *** | 15·56 | 21·83 | ** | 7·91 | 11·54 | |||||||
| ID × THERB | 11·86 | 10·84 | 8·72 | 12·83 | 13·98 | 11·98 | 8·79 | 13·62 | 15·53 | 55·27 | *** | |||||||||
| Season | 35·84 | ***M | 409·96 | ***M | 342·48 | ***M | 45·74 | ***A | 73·71 | ***A | – | 44·38 | ***A | 296·46 | ***M | 4·55 | *M | 68·42 | ***A | |
| Season × SR | 1·66 | 0·46 | 1·73 | 0·13 | 3·24 | – | 1·68 | 12·15 | *** | 3·59 | 18·04 | *** | ||||||||
| Season × LEG | 0·57 | 2·09 | 3·48 | 3·00 | 0·02 | – | 9·29 | ** | 0·13 | 1·37 | 11·50 | *** | ||||||||
| Season × SHERB | 6·31 | * | 1·24 | 0·11 | 0·05 | 0·24 | – | <0·01 | 0·71 | 0·23 | <0·01 | |||||||||
| Season × THERB | 0·35 | 0·42 | 0·23 | 6·68 | ** | 0·06 | – | 0·89 | 0·05 | 0·63 | 1·43 | |||||||||
| Season × ID | 30·58 | ** | 213·74 | *** | 117·79 | *** | 54·49 | *** | 172·39 | *** | – | 55·09 | *** | 53·77 | *** | 22·51 | * | 90·21 | *** | |
| (B) Legume presence prior to species richness | ||||||||||||||||||||
| LEG | 12·78 | *** ↓ | 9·49 | ** ↑ | 11·65 | *** ↑ | 32·91 | *** ↑ | 13·46 | *** ↑ | 1·23 | 6·45 | * | 9·89 | ** ↓ | 11·68 | *** ↓ | 21·74 | *** ↓ | |
| SR | 0·14 | 0·18 | 1·16 | 0·46 | 0·01 | 0·25 | 1·01 | 0·02 | 18·11 | *** ↓ | 11·84 | *** ↓ | ||||||||
| ID | 80·50 | *** | 212·25 | *** | 261·99 | *** | 151·13 | *** | 212·06 | *** | 139·39 | *** | 39·03 | *** | 28·30 | ** | 27·03 | ** | 157·39 | *** |
| ID × LEG | 18·12 | 19·69 | * | 33·26 | *** | 24·72 | ** | 53·21 | *** | 27·77 | ** | 13·30 | 16·78 | 49·04 | *** | 66·81 | *** | |||
| ID × SR | 17·95 | 16·26 | 11·65 | 20·78 | * | 12·02 | 33·12 | *** | 32·43 | *** | 38·50 | *** | 12·44 | 20·54 | * | |||||
| Season | 35·94 | *** | 409·79 | *** | 341·79 | *** | 45·79 | *** | 75·80 | *** | – | 44·01 | *** | 303·50 | *** | 4·29 | * | 73·07 | *** | |
| Season × LEG | 1·88 | 2·30 | 5·30 | * | 1·10 | 1·52 | – | 2·06 | 5·86 | * | 0·14 | 28·28 | *** | |||||||
| Season × SR | 0·25 | 0·18 | 0·01 | 2·11 | 1·69 | – | 8·93 | ** | 5·76 | * | 4·96 | * | 1·84 | |||||||
| Season × ID | 31·65 | *** | 214·81 | *** | 131·23 | *** | 54·26 | *** | 182·04 | *** | – | 51·25 | *** | 55·15 | *** | 21·37 | * | 81·44 | *** | |
Models were fitted by stepwise inclusion of the fixed effects. Likelihood ratios (L ratio) were used to assess model improvement and levels of significance are given (* P ≤ 0·050; ** P < 0·010;*** P < 0·001). For models in series (A) the species richness term was fitted prior to contrasts for the presence/absence of a particular plant functional group, while in model series (B) a contrast for the presence/absence of legumes was fitted before species richness.
Note that in series (A) contrasts for each plant functional group were tested in series of alternative models. Arrows indicate a significant increase (↑) or decrease (↓) of trait values in response to increasing species richness or the presence of a particular plant functional group.
(M) for May and (A) for August after the significance level for the term of season indicate that trait values were larger at the respective harvest date.
Abbreviations: SR = species richness (log-linear), LEG = legume presence/absence, THERB = tall herb presence/absence, SHERB = small herb presence/absence, ID = grass species identity.